The dormant buds of Rhabdopleura compacta (Hemichordata)

Rhabdopleura has an overwintering stage that consists of two layers of cells surrounding a central yolk mass. This cellular part is surrounded by a thick electron dense capsule which is secreted by the bud itself. The capsule is probably impervious and protective to its contents. Blood vessels join the buds to the zooids of the colony. They form the probable route of transfer of yolk from the zooids to the dormant bud. The capsule of the dormant bud has some structural features in common with the black stolon of the adult zooids. The black stolon is probably formed in a manner similar to that which made the fusellar fabric of the periderm of fossil graptolities.     

The ultrastructure of the tentacles of eleven species of dendrochirote holothurians studied with special reference to the surface coats and papillae

Summary The tentacles of eleven species of dendrochirote holothurians have been studied. The water vascular system, deep fibre system, ectoneural nerve ring and superficial fibre system are described and are similar to those of other holothurian tentacles. A conspicuous fuzzy coat covers the entire tentacular surface except for the tips of cilia. On the basis of its structure it is thought to be an attenuated glycocalyx. Its function is discussed in relation to anti-fouling and surface adhesion. The two surface coats underlying the fuzzy coat are termed the cuticle. Bacteria are found both within the surface coats and in the sub-cuticular space. Primary fixatives lacking osmium give poor preservation of the surface coats. The adhesive papillae of the apices of the tentacles contain elements of support cells and two other cells named Type-1 and Type-2 papillar cells. The secretions of Type-1 papillar cells are dense-cored vesicles and may contain a proteinaceous adhesive. The vesicles fuse with the cuticle and release their products which are apparently disseminated along the fuzzy coat filaments. The secretions of Type-2 papillar cells may have a neurosecretory function. The different models of food capture by dendrochirote tentacles are discussed as are duo-glandular adhesive systems in relation to dendrochirote tentacles.     

Ultrastructure of the grasshopper proximal femoral chordotonal organ

Summary Calpasoma dactyloptera, a tentacled form of minute, freshwater coelenterate, has been investigated by light and electron microscopy and time-lapse cinematography. Each tentacle consists of a protrusion from a single ectodermal epithelial cell termed a tentaculocyte. hin tentaculocyte vesicles which represent invaginations of the plasma membrane. A cnidocil protrudes into the external medium. The bottom of each nematocyte is elongated as a stalk which extends to the tentacle base, coursing through tubular membrane lined channels within the tentaculocyte. A network of fibers and microtubules, originating in the cnidocil, extends to the base of the nematocyte stalk.Supported by PHS Research Career Development Award 1-K04-GM42595 and NSF Research Grant GB 29284.     

Ultrastructure of the tentacles of the apodous holothurian Leptosynapta spp (Holothurioidea: Echinodermata) with special reference to the epidermis and surface coats

Summary The tentacles of the apodous holothurian Genus Leptosynapta have been studied by use of transmission and scanning electron microscopy. The gross anatomy, water vascular system, fibre systems and ectoneural nerve ring are described. A fuzzy coat of attenuated filaments covers the surface of the tentacle, broken only by secretory ducts. A cuticle underlies the fuzzy coat. Bacteria are common in the subcuticular space. Fixation without osmium gives poor preservation of the surface coats. The epidermis consists of a single layer of columnar cells consisting of Type-1, Type-2, support, goblet and uniciliated cells. Type-1 cells secrete electron-dense material and appear to be homologous to adhesive cells of the tentacles of other holothurians. The support cells contain large, granular vesicles not found in other holothurians. Goblet cells contain flocculent mucus and have an apical cilium. Goblet cells are not found in other holothurian tentacles and may function to lubricate and wrap adhering particles to aid their ingestion. The uniciliated cells are rare, poorly developed and the cilium does not extend past the cuticle. The ultrastructure of the tentacles is discussed in relation to those of other holothurians.     

Electron microscopic study on the gill bars of amphioxus (Brachiostoma californiense) with special reference to Neurociliary control

Summary Both primary and secondary (tongue) bars of the pharyngeal gill basket are covered by epithelial cells that are continuous with the cells that line the atrium. Anterior and posterior faces of the gill bars are covered with lateral ciliated cells, which possess a single cilium, ringed by microvilli, and an elaborate basal mitochondria-rootlet apparatus. Pharyngeal faces of the gill bars are covered with ciliated pharyngeal cells, atrial faces by mucus secreting atrial cells. The surface epithelium rests on a stromal septum, a flattened tube of basal lamina which dilates to form the visceral blood vessel (along the pharyngeal face) and skeletal blood vessel (along the atrial face). This basal lamina surrounds paired skeletal rods which run through the longitudinal axis of the gill bars near the atrial face. Between the skeletal rods and atrial cells of primary gill bars is a coelomic channel lined by epithelioid coelomic cells. Neuronal processes, some with neurosecretory granules, are located among the bases of the atrial cells. Some axons may contact lateral ciliated cells where the latter meet atrial cells, but synaptoid endings have not been found here or elsewhere in the gill bars. Nervous tissue has not been identified among lateral ciliated cells even though ciliary activity of these cells is supposedly regulated by atrial nervous tissue.Supported by a Cottrell College Science Program Grant from Research Corporation. We thank Nancy Kelly and Gerhard Ott for excellent technical assistance and are grateful for the facilities provided by the Department of Zoology and Seaver Science Center, Pomona College.     

Sensory innervation of the tentacles of the polychaete,Sabella pavonina

Summary Following observation of conical groups of stiff, but motile cilia on the tentacles of the branchial crown of Sabella pavonina, these were examined with the electron microscope. The bundles consist of about 40 unenclosed standard cilia supported by one or two primary sense cells with centrally directed axons of 0.1–0.2 diameter. Axons in the distal portions of the branchial crown occur in small bundles surrounded by a basement membrane. More centrally, glial elements appear and the nerves are surrounded by a collagenous sheath. The branchial nerve trunk shows similarities in organisation to other previously investigated annelid central nervous tissue in that the whole nerve is surrounded by a fibrous sheath central to which there is a layer of glial cells with processes penetrating a central neuropile. The 0.1–0.2 axons commonly occur in glial-enveloped groups of < 40 whilst other axons of larger and mixed diameter are found together.Each tentacle has two branchial nerves on the oral side, and each nerve gives rise to two small 75-axon branches running to each pinnule. The branchial nerves fuse to form the branchial nerve trunk running to the supra-oesophageal ganglia.Sections of the branchial nerves of the branchial crown at progressively more central levels show that the branchial nerve trunk contains enough axons of 0.1–0.2 diameter to account for all the sensory cells on the tentacles. This is taken as evidence for the sensory cells having axons terminating within the central nervous system and that there is no peripheral confluence or fusion of these afferent axons.     

The prosicular stage of Rhabdopleura (Pterobranchia: Hemichordata)

After settling, the larva of Rhabdopleura surrounds itself with a collagenous dome. Later, the zooid breaks through the wall of the dome and builds the horizontal tube part of the coenecium on to the dome.
The dome is a layered structure, unknown in other parts of the coenecium. whereas the horizontal tube is made up of rings in the classical manner of the adult coenecium. The construction of these two parts is different. The techniques used to reinforce the horizontal tube show a marked similarity to the cortical bandages recently described in the fossil graptolites, and give support to the claim that they are ancestral to Rhabdopleura. There are two sorts of early horizontal tube, one is a straight tube, and the other is longer and coiled. The hole in the dome through which the zooid emerges to build the horizontal tube is probably produced by a chemical boring of the zooid, and supports the hypothesis that the zooids can bore holes in shells and corals.     

The tentacles of Ichthyophis (Amphibia: Caecilia) with special reference to the skin

The skin of the paired tentacles of Ichthyophis consists of a cornified epidermis of 5–7 layers of epidermal cells, and a glandular dermis of ducted mucous glands, in association with collagen, blood vessels, fibroblasts, granulocytes, sparse melanophores and characteristic laminophores of unknown function. The epidermis is highly innervated at all levels below the stratum corneum by naked neurites, which originate as branches from large unmyelinated nerve bundles (and associated Schwann cells), located sub-epidermally, and which are part of the trigeminal cranial nerve. Myelinated nerves are also present below the epidermis, spatially associated with capillaries and glands. The study of the ultrastructure of the tentacle supports a concept of a sensory function, possibly tactile, though until further information from experimentation is available, any ideas on the specific nature of these sensory activities must remain speculative.     

An ultrastructural survey of the genus Prototheca with special reference to plastids

An ultrastructural investigation of six different species of Prototheca showed that all of them contained starch grains enclosed in double-membrane-bounded structures recognized as plastids. It is concluded that these unicellular species of Prototheca must be considered as non-photosynthetic algae.     

Ultrastructural studies on the ciliated receptors of the long tentacles of the giant scallop,Placopecten magellanicus (Gmelin)

Summary The long tentacles of the Giant scallop Placopecten magellanicus (Gmelin) have been examined with light, scanning, and transmission electron microscopy. Three types of ciliated cells have been observed, one of which is located in specialised papillae born on the distal third of the tentacle. There are two separate cell types within the papillae. Type I cells are non-ciliated supporting cells, which form a capsule within which are found the Type II cells. These cells bear up to five cilia at their apices, and it is suggested that these are the receptor cells of the organ. No function has yet been determined for the receptors, but is suggested that they might be mechanoreceptors. A third cell type, Type III cells, occur at the base of the papillae. These cells bear many cilia and also macrocilia. Another ciliated cell type occurs on the proximal two thirds of the tentacle. These cells bear many cilia that are thought to be motile and not sensory.This research was supported by National Research Council of Canada Operating Grant No. A-6444 to Dr. V.C. Barber. Additional support came from the Department of Biology and School of Graduate Studies, Memorial University. Contribution No. 249 from the Marine Sciences Research Laboratory, Memorial University of Newfoundland     

On the chromaffin cells in dog adrenal medulla; with special reference to the small granule chromaffin cells (SGC cells)

Small granule chromaffin cells (SGC cells) were identified in the adrenal medulla of adult dogs. They were small in size and usually showed a high nucleo-cytoplasmic ratio. Cytoplasmic projections were occasionally observed in some of these cells. They contained a variable number of small secretory granules with diameters ranging from 70 to 300 nm, but mostly from 100 to 200 nm. The densities of the secretory granules were variable, ranging from highly dense to less dense. These adrenal SGC cells were rich in free ribosomes and polysomes, but were relatively poor in other cell organelles. Chromaffin cells which were intermediate in their characteristics (IM cells) between the SGC cells and the typical A and N cells were also identified. These IM cells contained both highly electron dense and less dense granules in various proportions. The IM cells were classified into two subgroups, according to the proportions of adrenaline type granules and noradrenaline type granules. One group resembled A cells (IM-A cells) and the other resembled N cells (IM-N cells). Light microscopic histochemical studies of A cells stained with the ammoniacal silver solution demonstrated that they contained a small number of darkly stained granules. Electron microscopic cytochemistry revealed that the electron dense granuls in the SGC cells, IM cells and A cells reacted positively with both the potassium dichromate solution at pH 4.1 and the ammoniacal silver solution.     

An ultrastructural study of the dermal papulae of the starfish,Asterias rubens,with special reference to innervation of the muscles

Summary The ultrastructure of the dermal papulae of a starfish (Asterias rubens) is consistent with a respiratory function. The present study has shown no regions specialized for excretory mechanisms. The papulae consist of an outer ectodermal epithelium of sensory, support and gland cells and a small basiepithelial nerve plexus. A true basement membrane lies underneath the epithelium and regularly arranged longitudinal muscle bundles lie within the connective tissue. The coelomic cavity of the papulae is lined with ciliated endothelial cells, which overlie an irregular layer of circular muscles. A system of canals that are not lined by cells occurs at the base of the papulae with the circular muscles. The longitudinal and circular muscles show a different gross morphological arrangement and innervation. This paper proposes that there are skeletal and visceral types of smooth muscle in echinoderms and discusses this proposal at length.The author wishes to acknowledge with thanks the help of Miss Elaine Sneddon in the preparation of material for the electron microscope     

Interstitial cells associated with the deep muscular plexus of the guinea-pig small intestine,with special reference to the interstitial cells of Cajal

Summary Interstitial cells associated with the deep muscular plexus of the guinea-pig small intestine were studied by electron microscopy, and three-dimensional cell models were reconstructed from serial ultrathin sections with a computer graphic system. Three types of cells were recognized. The first type was similar in shape to smooth muscle cells, but did not contain an organized contractile apparatus. Many large gap junctions comprising about 4% of the cell surface were present; they connected cells of the first type to each other, to the second type of cell and to smooth muscle cells of the outer circular layer. The second type of cell had a welldemarcated cell body with long slender processes and was characterized by a large amount of glycogen comprising about 9% of the cell volume. The third type of cell was similar to fibroblasts, and contained well-developed Golgi apparatus and rough endoplasmic retiulum. Some of these fibroblast-like cells (a possible subtype) formed small gap junctions. All three types of cells showed close relationships with nerve varicosities. This cellular network consisting of gap-junction-rich cells, glycogen-rich cells and smooth muscle cells may be involved in the pacemaking activity of intestinal movement.     

Further studies of the surface epithelium covering preovulatory rabbit follicles with special reference to lysosomal alterations

Summary The fine structure of the surface epithelium over preovulatory rabbit follicles was examined parallel with visualization of acid phosphatase at the electron microscopical level. Small enzyme positive vesicles were pinched off from the Golgi cisternae and similar vesicles fused and got incorporated into larger lysosomes of dense body type. Some lysosomes appeared in direct continuity with tubular enzyme positive structures. Other possible ways of increase of the lysosomal pool are indicated and discussed.As in previous studies a maximal accumulation of lysosomes was found in the apical epithelium at 8 h after an ovulatory dose of human chorionic gonadotrophin (HCG); thereafter a gradual loss of lysosomes ensued. Before the lysosomes disappeared from the surface epithelium they changed in character. They became more electron-lucent and revealed a fine-fibrillar matrix. Dense bodies deep in the cell interior appeared to communicate with each other and with the extracellular space below the surface epithelium. Openings were never seen towards the peritoneal cavity. The loss of lysosomal content from the apical surface epithelium before follicle rupture appeared in many respects similar to the histamine release process in mast cells.The findings support our working hypothesis that the surface epithelium over Graafian follicles is an essential source of proteolytic enzymes and that these may be released extracellularly and actively contribute to the dissolution of the follicular apex before rupture.This investigation was supported by grants from the Swedish Medical Research Council (Projects No. B74-12X-78-09C and B75-12X-78-10A). The technical assistance of Miss Ingalis Fransson and Miss Kerstin Nilsson is greatly appreciated     

Structural alterations of rabbit ovarian follicles after mating with special reference to the overlying surface epithelium

Summary Rabbit ovarian preovulatory follicles and in particular the overlying surface epithelium were studied by morphological and ultrahistochemical means at different times after mating.By light microscopy an increase of cytoplasmic granules was found in the surface epithelium at the follicle apex 4 h after mating. The granules increased in amount and showed maximal accumulation 8–9 h after mating. They then disappeared at the same time as the connective tissue elements in the underlying tunica albuginea and theca externa disintegrated.Transmission electron microscopy showed that the membrane-bounded granules or dense bodies fused with one another and by 8 h after mating they often changed character and appeared more electron lucent. Furthermore, open communications were found between altered granules and vacuoles and between vacuoles and the extracellular space below the epithelium. Acid phosphatase reaction product was localized to the granules and Golgi cisternae. Not all the dense bodies were enzyme positive. At later stages, close to the time of follicle rupture, the epithelial cells were attenuated and thin, with only a few granules.By scanning electron microscopy it was found that the epithelial cells at the follicle apex increased in size approaching the time of follicle rupture and that their microvilli decreased in number and in size. At 8 h and later, the contours of intracellular granules could be visualized.The results of this study were similar to those found when rabbits were induced to ovulate by HCG-stimulation. This further strengthens the hypothesis that the surface epithelium contributes proteolytic enzymes which help to disintegrate the follicle apex prior to rupture.     

A study of cells present in peripheral lymph of pigs with special reference to a type of cell resembling the langerhans cell

Summary Large mononuclear cells with long, actively moving cytoplasmic veils were observed in lymph coming from the skin. The enzyme histochemistry and ultrastructure of these cells suggested that they are related to epidermal Langerhans cells and interdigitating cells in the lymph node. It has been reported that Langerhans cells and interdigitating cells play a role in contact hypersensitivity by taking up antigen and presenting it to thymus-dependent lymphocytes, and it is likely that the veiled cells in the lymph are also involved.After skin-painting with 1-fluoro-2,4-dinitrobenzene (DNFB), the veiled cells in lymph coming from the site of painting became more active and were observed contacting other cells present in the lymph; many large cellular aggregates were found. Since neutrophilic leucocytes and mononuclear phagocytes were the predominating cell types in this lymph, there was no evidence for a massive recruitment of immunocompetent lymphocytes at the site of painting.Neonatally thymectomized pigs do not develop allergic reactivity to DNFB. It is of interest that the number of veiled cells and their ability to form large cellular aggregates was not affected in these animals. Therefore, it is unlikely that the defect in responsiveness can be attributed to a failure in the function of veiled cells.     

The proventriculus of the carpenter bee, Xylocopa virginica virginica (L.), with special reference to bacteria-containing luminal tunnels

Abstract. Four tunnels off the lumen of the proventriculus of the carpenter bee, Xylocopa virginica virginica , have been discovered. Light and electron micrographs revealed the presence in the tunnels of gram-positive, rod-shaped bacteria, some of which showed division stages. The occurrence of the bacteria exclusively in the tunnels—not in the lumen of the proventriculus—makes speculation as to their function difficult. The function of the tunnels is also obscure, as no glands were seen emptying into them. The bacteria may be symbionts that release enzymes into the tunnels, which are subsequently transported to the midgut to aid digestion. They could also be parasites. This is the first report of such bacterial-containing tunnels in insects.     

Crystalloid structures within giant mitochondria of the prothoracic glands of Spodoptera littoralis (Bois) (Lepidoptera)

The fine structure of the prothoracic glands of Spodoptera littoralis was investigated during the first half of the last larval instar. The secretory cells have two types of mitochondria, micromitochondria and macromitochondria. The micromitochondria have rounded to elongated profiles and sometimes branch. They contain lamellar, tubular and also tubulo-vesicular cristae. The macromitochondria appear generally rounded or oval and possess tubular cristae. Many regular parallel membranes appear within macromitochondria. Favorable sections show tubular structures packed in honeycomb fashion. The mitochondrial cristae are in connection with the tubular structures. Honeycomb and parallel membranes increase in number as the size of the macromitochondria increases.     

The distribution of monoamines in the tel-, di-and mesencephalon of Xenopus laevis tadpoles,with special reference to the hypothalamo-hypophysial system

Summary In an attempt to further our knowledge about the structure and function of the recently identified intrapulmonary Neuro-epithelial Bodies (NEB's) (Lauweryns et al., 1972a, 1972b), lungs of 84 neonatal rabbits and 6 neonatal mice were studied along four different lines of investigation. Several routine and silver staining methods, Falck's fluorescent amine technic and histochemical and electron microscopical techniques were performed.1. In order to test the probable chemoreceptor function of the NEB's, animals were exposed to hypoxia. Under such circumstances, the corpuscular cells of the NEB's secrete their dense-cored, serotonin-containing vesicles at their basal vascular pole. 2. After reserpine pretreatment, the NEB's of otherwise normal animals reveal a distinct amine depletion, the corpuscular cells exhibiting a decreased yellow fluorescence and ultrastructurally a clearing up of their dense-cored vesicles. 3. Studied on serial sections with the electron microscope, various types of morphologically afferent-like and efferent-like nerve endings, making contact as well with the corpuscular cells as amongst themselves have been detailed. 4. Cytochemically the corpuscular cells react positively with alpha-glycerophosphate dehydrogenase, acetylcholinesterase and Solcia's lead hematoxylin stain for endocrine cells producing polypeptides and amines.It is proposed that the NEB's provide an intrapulmonary, hypoxia-sensitive neuro(chemo-) receptor system in addition to the well established central and peripheral (e.g. carotid body) chemoreceptors. They contain and secrete serotonin and probably also related amines or peptides, which could influence the pulmonary vasoconstrictor response. According to classic morphologic criteria, they possess a dual innervation, both afferent and efferent.Various other possible functions of the NEB's in normal and diseased lungs are briefly proposed.This study has been supported by a grant from The Council for Tobacco Research — U.S.A. and the Nationaal Fonds voor Wetenschappelijk Onderzoek — Belgium. We thank P. Theunynck for performing some of the histochemical studies, B. Van Rijkel, B. Emanuel and R. Renwart for technical, G. Pison and St. Ons for photographical and N. Tyberghien for secretarial assistance.