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Because the urinary bladder stores and releases urine, its normal function includes filling and emptying, accompanied by distension and relaxation. It is known that chronic distension compromises blood flow. Recent studies of the rabbit bladder vasculature have described specializations of that vasculature that appear to enhance blood flow in the bladder wall during distension. The present report describes the location, orientation, and structure of an elastic sheath surrounding the vesicular arteries, which may represent one of these specializations. The location, vasculature, and structure of an accessory elastic sheath surrounding the vesicular arteries of the rabbit bladder is described using light and electron microscopy, India ink injection, and vascular corrosion casting. The common iliac arteries of rabbits were cannulated to permit perfusion of the distal vasculature including the urinary bladder. After the bladder vasculature was visually cleared of blood by perfusion with buffered saline, one of the following procedures was used: 1) for light or electron microscopy, the bladder was perfuse-fixed with buffered 2% glutaraldehyde; 2) the bladder vasculature was filled with India ink for vessel tracing; or 3) corrosion casts of the bladder vasculature were prepared by infusion of a Mercox resin mixture. Casts, cleaned of tissue with KOH, and water and formic acid rinses, are dried, and mounted for routine scanning electron microscopy. The presence of an accessory sheath surrounding the main vesicular arteries and some of their branches in the basal two thirds of the urinary bladder was observed on India ink injected specimens and confirmed by micrographs and vascular corrosion casts. The sheath consists of elastic and collagenous fibers and is separated from the tunica media of the arteries by a loose connective tissue layer of variable width. The sheath is circumscribed by a layer of fine blood vessels. The vesicular arteries undulate within the sheath to an extent which is dependent upon the degree of distension of the bladder. This sheath likely represents a specialization which permits the bladder vasculature to accommodate expansion and contraction of the wall during normal filling and emptying. Undulations or coiling of the vesicular arteries within the loose connective tissue core of the sheath increase with bladder contraction, and apparently the sheath simply holds the artery in position during such coiling. The sheath, may represent a modification of the external elastic lamina found in some muscular arteries.

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The urinary bladder is especially subject to infection by virtue of its direct connection to the external urethral opening, and it is natural to anticipate the presence of a well-developed immunological mechanism to respond to this potential threat. The present study describes small, very highly vascular lymph nodes located in the wall of the rabbit bladder, which may be involved in a local response to foreign antigens. The vasculature and structure of these lymph nodes was described using a combination of vascular corrosion casting, ink injection, and light and electron microscopy. The distal abdominal aorta was cannulated, and after clearing the bladder vasculature with buffered saline, one of the following procedures was used: 1) the bladder was perfuse-fixed in preparation for light and electron microscopy; 2) the bladder vasculature was filled with India ink for vessel tracing; or 3) vascular corrosion casts of the vasculature were prepared by infusing resin comprised of a mixture of Mercox, methyl methacrylate monomer, and catalyst. The resulting casts were cleaned with KOH, formic acid, and water in preparation for scanning electron microscopy. Vascular casts and India ink injections revealed the presence of a number of isolated capillary tufts consisting of clusters of one to five "glomeruli," closely associated with the major vesicular vessels along the lateral walls of the bladder, and supplied by tertiary branches of these vessels. Light and electron microscopy showed that the capillary tufts represented the blood supply to small, ovoid lymph nodes located near the serosal surface of the bladder wall and usually restricted to the basal half of the bladder. These nodes were encapsulated and exhibited subcapsular sinuses, numerous small blood vessels, a limited number of high endothelial cells, and, occasionally, nerves and a follicular substructure. The nodes contained abundant lymphocytes, stellate stromal cells, macrophages, and eosinophils, but lacked the obvious cortical and medullary organization and germinal centers often seen in larger lymph nodes. Vascular corrosion casts, vascular ink injections, and microscopic examination confirmed the presence of small, highly vascular lymph nodes closely associated with the main vesicular vessels along the lateral walls of the rabbit bladder. A follicular substructure of the nodes appears to correspond with the "glomerular" capillary arrangement within the nodes as seen with corrosion casts. The rich blood supply may be indicative of the high metabolic demand of lymphatic tissue, and may be altered in response to the level of activity of the node. The close association between the lymphatic tissue and the rich blood supply to the nodes may allow a rapid mobilization of lymphocytes during a local immune response to foreign agents.

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BACKGROUND: The urinary bladder requires a rich blood supply to maintain its functions, the storage and release of urine. Specialized properties of the bladder vasculature might be anticipated to ensure the integrity of this blood supply, because it is known that blood flow is reduced by distension during bladder filling. However, the bladder vasculature has been described in detail only at the gross level. A comprehensive, three-dimensional view of the blood supply to the bladder wall is presented here. METHODS: The microvasculature of the bladder of male New Zealand white rabbits was described using the combination of vascular corrosion casting, alkali digestion, light microscopy, and scanning and transmission electron microscopy. Following administration of an anticoagulant and an overdose of anesthetic, the abdominal aorta was cannulated just above the inferior mesenteric artery to permit flushing of the distal vasculature. The bladder vasculature was cleared of blood with buffered saline and then either perfuse-fixed with buffered 2% glutaraldehyde and sectioned, or filled with "Mercox" resin to prepare vascular corrosion casts. Casts were cleaned with NaOH, formic acid, and water. In some cases fixed bladders were partially digested with NaOH to expose the mucosal capillary plexus. RESULTS: The bladder is supplied with blood by single, left and right vesicular branches of the internal or external iliac arteries. The serpentine vesicular arteries extend along the lateral borders of the bladder from base to apex just deep to the serosal surface and send dorsal and ventral branches to supply the dorsal and ventral bladder walls. Veins accompany the arteries and exhibit numerous valves. A very dense complex of vessels at the apex of the bladder apparently serves to accommodate bladder distension. The muscularis and submucosa contains few vessels, but the mucosa is well vascularized. An especially dense capillary plexus is present in the lamina propria at its junction with the transitional epithelium. In the relaxed bladder these capillaries lie in grooves formed by the basal layers of the epithelium. The endothelial cells of these capillaries display few cytoplasmic vesicles and are continuous or fenestrated. These capillaries are often invested with pericytes. The mucosal capillary plexus may be associated with an epithelial transport function or may be necessary for urothelial metabolism or maintenance of the barrier function of the urothelium. Unusual capillary tufts, possibly associated with vascular lymphatic tissue, are found associated with the main vessels on the lateral walls in the basal half of the bladder. CONCLUSIONS: These methods present a clear, comprehensive, three-dimensional view of the microvasculature of the bladder wall. They also identify several unique features of this vasculature and provide a basis for studies of the response of this vasculature to pathologic states and experimental manipulation.

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BACKGROUND: The success of kidney transplant surgery and ureteral reconstruction requires the preservation of the ureteral blood supply. Because of its potential vulnerability to surgical trauma during transplant and reconstructive surgery, the ureteral vasculature merits a full anatomical description. METHODS: The microvascular anatomy of the ureter was studied in male New Zealand white rabbits by light microscopy and transmission electron microscopy and scanning electron microscopy of vascular corrosion casts and alkali digested tissue. RESULTS: The rabbit ureter is supplied predominantly by a branch of the renal artery proximally (cranial ureteral artery) and by a branch of the vesicular artery distally (caudal ureteral artery). Minor vascular continuities are also present between the capillary beds of the ureter and those of the renal pelvis cranially and the bladder wall caudally. There are no external vascular connections to the middle ureter with the exception of a single, small vein which drains into the inferior vena cava. A single group of longitudinal arteries and veins runs the full length of the ureter within the adventitia. Branches of these longitudinal vessels pass tangentially through the muscularis to supply a vascular complex within the lamina propria. This complex in turn supports a rich, mucosal capillary plexus located at the junction between the transitional epithelium and the lamina propria. In the fixed ureter the capillary plexus lies in grooves formed by displacement of the basal layers of the overlying transitional epithelium. The capillaries are continuous or fenestrated, are often invested with pericytes, and are distributed uniformly around the entire circumference of the ureter. CONCLUSIONS: The ureteral vasculature exhibits several unique features related to its function in urine conduction and its ability to accommodate expansion and contraction. The combination of techniques used provides a clear three-dimensional view of this vasculature. Our findings also confirm that, because of its limited blood supply, the ureter may be very susceptible to injury during renal transplantation or other abdominal surgery.

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To help define the optimal conditions for the preparation of vascular corrosion casts of rat heart, we examined the effect of prefixation with aldehyde fixatives on the perfusion rates of rat heart and on the quality of vascular casts. For these studies, beating hearts were removed from rats, cannulated via the aortic stump, arrested with KCl, perfused retrograde with buffered saline or fixative, and infused with resin to prepare corrosion casts. Fixatives used were 2.5% glutaraldehyde or 2% paraformaldehyde, and the casting resin consisted of a Mercox-methylmethacrylate mixture (4:1). All perfusion pressures were monitored at 80 to 100 mm Hg using a mercury manometer. The perfusion rate of control hearts was 13 to 14 mL/min. Prefixation with glutaraldehyde and paraformaldehyde reduced perfusion to 8.5 and 8.1 mL/min, respectively. Cast quality was observed grossly and with the scanning electron microscope. Control hearts yielded high quality, complete casts with 2570 capillaries/mm(2+). Casts from prefixed hearts exhibited areas of incomplete vessel filling and resisted complete tissue maceration, leaving tissue remnants adhering to the vessel replicas. Casts from glutaraldehyde-fixed hearts were of very poor quality. Our results indicate that prefixation is an unnecessary step in the preparation of vascular casts of rat heart and is inconsistent with cast quality.

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The transmembrane potential (Vm) of vascular endothelial cells (EC) is an important property that may be involved in intra- and intercellular signal transduction for various vascular functions. In this study, Vm of intact aortic and vena caval EC from hamsters were measured using conventional microelectrodes. Vascular strips with the luminal surface upwards were suffused in a tissue chamber with Krebs solution in physiological conditions. The resting Vm of aortic and vena caval EC was found to be -40 +/- 1 mV (n = 55) and -43 +/- 1 mV (n = 15), respectively. The Vm recordings were confirmed to have originated from EC by scanning and transmission electron microscopy combined with the comparison of electrical recordings between normal and endothelium-denuded aortic strips. The input resistance varied from 10-240 M omega, which implied the presence of electrical coupling between vascular EC. Elevating the K+ level in the suffusate from 4.7 mM to 50 and 100 mM depolarized aortic EC by 19% and 29% and vena caval EC by 18% and 29%, respectively. These low percentages indicated a relatively small contribution of [K+] to the resting Vm of vascular EC. A positive correlation (r > 0.69) between the resting Vm and the magnitude of depolarization by the high [K+]o may be related to the involvement of voltage-dependent K+ channels. The hyperpolarization caused by lowering both [Na+]o and [Cl-]o suggested the disengagement of some electrogenic transport systems in the membrane, such as a Na(+)-K(+)-Cl- cotransporter. The transference number (t(ion)), as an index of membrane conductance for specific ions, was calculated for K+ (15-20%), Na+ (16%), and Cl- (9-15%), demonstrating that both Na+ and Cl- as well as K+ contribute to the overall resting Vm. Our study documented some basic electrophysiology of the vascular EC when both structural and functional properties of the cell were maintained, thus furthering the understanding of the essential role of endothelial cells in mediating vascular functions.

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Effects of neurokinin A (NKA) and substance P (SP) on coronary resistance vessels were studied in isolated guinea pig hearts perfused with isotonic buffer containing 20 mM KCl. Injections of NKA and SP caused dose-dependent reductions in perfusion pressure with ED50 values of 14.0 and 0.326 pmol, respectively. Blockade of nitric oxide synthesis or removal of the endothelium inhibited vasodilator responses to neurokinins. Infusions of NKA or SP caused tachyphylaxis and cross-desensitization to the other neurokinin but not to acetylcholine. Injections of 2.5 nmol NKA increased perfusion pressure by 31 +/- 8% when given after tachyphylaxis developed to infused SP (2.5 nmol/100 microliters/min). It was concluded that 1) neurokinins cause an endothelium-dependent relaxation of coronary resistance vessels by stimulating NK-1 receptors on endothelial cells, and 2) desensitization of the receptor mediating vasodilation unmasks a vasoconstrictor response to NKA.

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Retia mirabile of the eel swimbladder were exsanguinated, perfusion-fixed and subjected to prolonged osmication. They were then microdissected by ultrasonication which delaminated the capillary bed along planes which revealed the surfaces of arterial and venous capillaries. This procedure resulted in cleaned capillary surfaces largely free of connective tissue elements and basement membrane material. The arterial capillary segments were heavily invested with pericytes characterized by plump cell bodies containing nuclei and an extensive system of processes encircling the capillary wall. These processes exhibited a hierarchical organization consisting of primary, secondary, and tertiary elements arising roughly at right angles to each other. Primary and secondary processes exhibited frequent anastomoses and resulted in cytoplasmic continuity between adjacent cell bodies. Processes were also observed to form connections between pericytes on adjacent capillaries. These observations are evidence for the existence of a pericapillary syncytium in which cell bodies may be connected in series and in parallel throughout the arterial capillary bed. This syncytial organization would provide for a coordinated and global contractile response of pericytes to vasoactive hormones and other effectors. It may also provide for synchrony of nuclear division during developmental spread of pericytes along capillary surfaces.

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The surface morphology of transplants of rat fetal hippocampal tissue, and of cavities formed by aspiration lesion of the adult rat hippocampus and overlying neocortex into which the transplants were placed, was studied by scanning electron microscopy. The surface of lesion cavities was covered by a scar upon which occasional cellular profiles were found. The surface cells resembled supraependymal macrophages. Lesion cavities with a transplant showed similar scarring although the number of supraependymal structures was increased. Polymorphic cells and numerous fiber processes were observed both on the surface and embedded in the scar. Ependymal structures were seen on the non-damaged ventricular surfaces adjacent to the lesion site. These regions, however, also displayed increases in the number and types of supraependymal structures. Scanning electron microscopy demonstrated considerable variability in surface morphology of different transplants and over the surface of individual transplants. A transplant could show regions of scarring, areas covered by cells resembling ependymal cells, and regions covered by a dense matrix of fibers. In many regions the fibers coalesced to form a branching, web-like network over the transplant surface. Transmission electron microscopy indicated that the surface could be covered by ependymal cells or by the scar seen in scanning specimens. Some surface fibers were identified as axons. Cells on the surface of the transplants could be identified as neuronal, glial-like, and phagocytic. The cells and the possible effects of surface morphology on transplant function is discussed.

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Vascular corrosion casts of normal and elastase-induced emphysemic hamster lungs, prepared with a low viscosity resin mixture consisting of Mercox and Sevriton, were observed by scanning electron microscopy. Casts were quantitated by measuring vascular volume or determining non-alveolar air space using confocal laser scanning microscopy. Normal lung casts were characterized by well-organized fields of alveoli (about 70 microns in diameter) connected by distinct alveolar ducts. Emphysemic lung casts exhibited numerous bullae (often as large as 0.5 mm in diameter). The vasculature of the bullae indicated that they were formed by destruction of alveolar walls and subsequent coalescence of numerous alveolae. Remnants of alveolar walls, consisting of shallow ridges of capillaries, lined the bases of the bullae. Vascular volumes expressed as cast volume/total tissue volume were calculated at 20% and 12% for uninflated and inflated lungs, respectively, for both control and emphysemic lungs. Four months after elastase instillation, nonalveolar air space of the emphysemic lungs was increased by 73% over controls. These observations indicate that elastase emphysema results, initially, in remodeling of the alveolar structure (bullae formation) and loss of surface area for gas exchange, rather than from extensive loss of vasculature. Vascular corrosion casting is a useful technique for monitoring emphysema both morphologically and quantitatively.

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The three-dimensional microvasculature of the nasal salt gland of the duckling was studied by vascular corrosion casting and scanning electron microscopy. Changes in the vascular volume of the gland in response to osmotic stress were also determined using cast weights and densities. The richly vascularized gland is supplied on its medial surface by large branches of the supraorbital and ethmoidal arteries. Numerous arterial branches enter the gland and distribute to lobes via the interlobar connective tissue. Lobar arterioles penetrate to the periductal areas of the lobes before dividing into capillaries supplying the ductal epithelium and secretory tubules. Capillaries envelope the secretory tubules and run radially from the ducts toward the lobe periphery, so that blood flows counter to the tubular secretion. Blood is collected via venous plexuses seen as distinct drainage units on the periphery of each lobe. Veins exhibit large numbers of bicuspid valves. Following 1 day and 4 days of osmotic loading (feeding 1% NaCl), vascular volume of the gland increased fivefold and ninefold, respectively, a response that precedes and exceeds that of the gland weight or Na,K-ATPase activity. When salt water-adapted ducklings were fed fresh water for only 24 hr (deadaptation), vascular volume fell to 2.8 times the control level. Changes in blood flow to the gland during osmotic adaptation and deadaptation are rapid and dramatic and may represent the initial steps in the control of gland secretion.

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After induction of experimental polymicrobic osteomyelitis with Staphylococcus epidermidis and Bacteroides thetaiotaomicron (ciprofloxacin MIC, 0.5 micrograms/ml and 4.0 micrograms/ml, respectively), in the presence of a foreign body implant, in a rabbit tibia model, ciprofloxacin was administered to infected animals for 2- and 4-week periods. At necropsy, rabbits in the 2-weeks-treated group had mean ciprofloxacin levels of 5.94 micrograms/ml in serum, 3.63 micrograms/g in marrow, and 1.88 micrograms/g in bone. Rabbits in the 4-weeks-treated group had mean ciprofloxacin levels of 7.77 micrograms/ml in serum, 5.84 micrograms/g in marrow, and 2.01 micrograms/g in bone. Quantitative bacterial plate counts were conducted on weighed samples of infected bone, marrow, and the catheter implant, taken at necropsy from treated and control rabbits. Variable reduction of bacterial numbers was observed in samples from treated animals, as compared to untreated controls. Samples of infected bone, marrow and catheter, showed comparable evidence of osteomyelitis and bacterial colonization in both treated and control animals. Although relatively high tissue levels of ciprofloxacin were attained, little therapeutic effect was observed.

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The anatomy and morphometry of venous values associated with the vasculature of the head of the duckling were studied using vascular corrosion casting and scanning electron microscopy. All valves encountered were bicuspid, and casts typically exhibited slight expansions at valve sinuses and deep slits at the sites of valve leaflets. The locations, numbers, and orientations of endothelial nuclei on all surfaces of the valves were clearly revealed by imprints in the casting resin. Endothelial cell densities were significantly higher on the surfaces of valve leaflets (about 10 cells/1,000 micron2) than on other venous surfaces (about 7 cells/1,000 micron2). Endothelial nuclei on the medial surface of the valve leaflet were oriented parallel to the long axis of the vessel, whereas those on the lateral surface were oriented perpendicular to that axis. The close proximities of valves in some vessels and the presence of anomalies such as the sharing of leaflets by adjacent valves were readily demonstrated with the corrosion-casting techniques. These methods provide a useful means for studying the fine, three-dimensional details of venous valve anatomy.

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The ultrastructure of the surface epithelium and the associated basal lamina of the gill arches of the striped bass, Morone saxatilis, were investigated with the scanning electron microscope following complete or partial removal of the epithelium by ultrasonic microdissection. The microdissection procedures employed various combinations of the techniques of aldehyde fixation, treatment with borate, and extensive osmication followed by mild sonication. Generally, aldehyde fixation increases intercellular adhesion, excess osmication increases tissues brittleness, and borate treatment causes extensive tissue dissociation. However, the degree of epithelial removal following sonication of tissues treated with these various procedures varies considerably with specimen structure, shape, proximity to adjacent structures and freedom to vibrate during sonication. The basal lamina exhibits a smooth contour over most of the gill surface with the exception of the short gill rakers where it formed cones within the taste bud cores, and on the respiratory lamellae where it closely mimicked the underlying capillary network.

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The retea mirabilia are paired capillary organs located on the dorsal surface of the swimbladder of the common eel. They consist of bundles of closely apposed capillary segments which function in countercurrent exchange of gases and other solutes and concentrate oxygen in the swim bladder. Ultrastructural features of the afferent arterial capillaries and efferent venous capillaries were studied by scanning EM of corrosion casts and critical-point dried retes and transmission EM of thin sections and freeze-fractured retes. A loose association between endothelial cells in the venous capillaries is indicated by penetration of casting material into interendothelial clefts and the appearance of clefts bounded by cytoplasmic flaps in exposed critical-point dried specimens. In thin sections, open gaps between venous endothelial cells are bounded by cytoplasmic processes. Sections through arterial capillaries exhibit tight occluding junctions joining endothelial cells together and these can be seen in freeze-fracture replicas to extend without interruption along the length of the arterial capillaries. These studies indicate the absence of open or hydraulically conductive pathways across the arterial capillary walls and that they probably constitute a rate-limiting barrier in countercurrent exchange of solutes.

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The present paper describes a procedure for preparing vascular corrosion casts of rat myocardial microvasculature. Essential components of the procedure include: partial "self clearing" of the heart in vitro; cardiac arrest by infusion of KCl; retrograde aortic root infusion of Mercox-Sevriton casting resin; KOH digestion of ventricular tissue; and desiccation and mounting of casts for scanning electron microscopy. About 50% of rats yielded complete casts. Vasculature closely paralleled muscle fiber orientation. Capillary beds characteristically exhibited branching, many intercapillary cross bridges, and occasional coiling. Average capillary cast diameter (5.6 microns) and intercapillary distance (15 microns) are comparable to results from in vivo studies. From preliminary calculations, vascular volume represents about 10% of the ventricular walls. These data indicate that vascular corrosion casts may be useful in the analysis of pathologic states and in determining the role of potential therapeutic interventions.

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At 3-month intervals from birth to 27 months of age, 3 female armadillos were killed. The number and size of follicles greater than 202 micron were determined, plasma progesterone concentration was measured, and values were correlated with age. Blood samples were taken monthly by femoral vein puncture and plasma was analysed by radioimmunoassay for progesterone concentration. At necropsy, both ovaries were visually inspected for a corpus luteum, weighed and then processed for routine histology. The number of normal, antral follicles greater than 202 micron were counted. These follicles were arbitrarily categorized into 15 different size groups (every 77 micron). Total number of follicles greater than 202 micron varied from 15.5 +/- 1.3 at 15 months of age to 26.3 +/- 1.9 at 21 months. Follicles of a size (greater than 978 micron) most likely to ovulate were present only at greater than or equal to 9 months of age. Progesterone values remained below the adult concentration (5 ng/ml) until 15 months of age. A concentration of progesterone indicative of ovulation (approximately 10 ng/ml) occurred between 17 and 20 months of age. The findings of the present study demonstrate that the female armadillo is reproductively mature after 15 months of age.

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The avian salt gland provides an ideal system for the study of plasma membrane (PM) biogenesis. Feeding ducklings 1% sodium chloride (salt stress) induces the secretory cells of the gland to synthesize large amounts of PM, which forms an extensive basolateral PM domain after 7-9 days of treatment. In the present study, the initial biosynthetic events following salt stress were investigated. In vivo studies using 3H-uridine indicated that increased rates of RNA synthesis could be detected by 2 hr after the beginning of salt stress and continued through at least 12 hr. Under in vitro conditions, increased rates of protein and glycoprotein synthesis (as monitored by 3H-leucine and 3H-fucose incorporation, respectively) were also detected after 2 hr and continued through 7-9 days. Increased levels of Na,K-ATPase, a specific secretory cell PM marker, were detected after 8 hr of treatment as monitored by specific activity and 3H-ouabain binding. Sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis coupled with fluorography indicated that both 3H-leucine and 3H-fucose were incorporated into partially purified preparations of Na,K-ATPase isolated after 12 hr. Light microscopic autoradiographic analysis of pulse-chase experiments indicated that in secretory cells of 12-hr salt-stressed glands, 3H-leucine- and 3H-fucose-labelled products reached the cell periphery by 1-2 hr after the initial pulse. The incorporation of both tritiated precursors was predominantly associated with the secretory cells. Quantitative electron microscopic autoradiography indicated that 3H-leucine is initially taken up by elements of the rough endoplasmic reticulum (RER) and cytoplasm (5 min postpulse), subsequently transported to and concentrated within components of the Golgi apparatus (10 min of chase), and ultimately incorporated into all domains of the plasma membrane of secretory cells by 1-2 hr of chase. The data is consistent with a flow of newly synthesized membrane components from RER to Golgi to plasma membrane and is analogous to the pattern previously found for the synthesis and processing of PM proteins in a wide variety of cell types.

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The surface ultrastructure of the gill arches of the killifish, Fundulus heteroclitus, adapted to seawater or freshwater, was found to be similar to that reported for other euryhaline teleosts. Two rows of gill filaments (about 42 filaments per row) extended posterolaterally, and two rows of gill rakers (about 10 rakers per row) extended anteromedially from each arch. Leaf-like respiratory lamellae protruded along both sides of each filament, from its base to its apex. The distributions, sizes, and numbers of various surface cells and structures were also determined. All surfaces were covered by a mosaic of pavement cells, which measured about 7 X 4 microns and exhibited concentrically arranged surface ridges. Taste buds were especially prominent on the rakers and the pharyngeal surfaces of the first and second gill arches, but were often replaced by horny spines on the third and fourth gill arches. Apical crypts of chloride cells occurred mostly on the surfaces of the gill filaments adjacent to the afferent artery of the filament. In seawater adapted killifish, crypts resembled narrow, deep holes along the borders of adjacent pavement cells, had openings of about 2 microns2, and occurred at a frequency of about 1 per 70 microns2 of surface area. In freshwater fish, the crypts usually had larger openings (about 10 microns2), occurred less frequently (1 per 123 microns2), and exhibited many cellular projections in their interiors. Changes in crypt morphology may be related to the ion transport function of chloride cells.

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The microvasculature of the eye of the duckling was studied with microcorrosion casting, scanning electron microscopy, and stereology. Most blood to the eyeball first passes through the arterial ophthalmic rete mirabile, a complex of small arteries which intermixes with a similar complex of veins (venous ophthalmic rete mirabile) at the ventrotemporal angle of the eye. The present study reveals the ultrastructural anatomy and the compact, three-dimensional arrangement of vessels in this rete, which had been shown by previous investigators to function as a countercurrent heat exchanger. Vessels from this rete include the supraorbital and infraorbital arteries, which supply the eyeball anteriorly, and the ophthalmotemporal artery, which supplies the eyeball posteriorly. The internal ophthalmic and ethmoidal arteries, branches of the cerebral carotid artery, anastomose with the ophthalmotemporal artery posteriorly. Blood is distributed to the eyeball anteriorly by two ring arteries: the iridial ring artery, which circumscribes the iris and which receives blood from the long ciliary and infraorbital arteries; and the more peripheral, ciliary ring artery, which receives blood mostly from the infraorbital and ethmoidal arteries. Within the iris is a dense, freely anastomosing bed of capillaries which extends to the edge of the pupil and then loops back beneath the ciliary body. The vasculature of the ciliary body consists of radially arranged plates of anastomosing capillaries of irregular bore which mimic the contours of that organ, but permit changes in pupil diameter. The present study demonstrates the three-dimensional anatomy of the very dense capillary net of the choriocapillaris deep to the retina and the capillary mass of the pecten, and thus supports the finding of earlier investigators that nutrients diffusing from these structures nourish the avascular retina. The pecten consists of a pleated sheet of freely anastomosing capillaries which protrudes into the vitreous body from near the optic nerve. The choriocapillaris and the pecten are supplied by branches of the ophthalmotemporal artery: the former by numerous short posterior ciliary arteries, the latter by two or three arteries which further divide into one or two smaller vessels for each of its folds. Veins of the choroid layer at the periphery of the anterior surface of the eyeball, and to some extent on its lateral walls, are revealed by the corrosion-casting technique as unusual, flattened vessels of large caliber which lie in closely spaced parallel arrays. The large surface area thus created may function in heat dissipation.(ABSTRACT TRUNCATED AT 400 WORDS)

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