Electron microscopic study on the epiplexus (Kolmer) cells of the cat choroid plexus

Summary A light and electron microscopic study was made of the epiplexus (Kolmer) cells of the cat choroid plexus. These polymorphic, motile cells were typically found juxtaposed to the ventricular surface of the choroidal epithelium. They have many ultrastructural features in common with free macrophages of other systems, namely, an indented nucleus with condensed chromatin, sparse mitochondria and endoplasmic reticulum, free ribosomes, multiple Golgi elements, microtubules, coated surface invaginations and microvesicles, and numerous membrane-limited vacuoles and lysosomal dense bodies. A unique feature of epiplexus cells is the manner in which they are anchored to the choroidal epithelium by the invagination of their surfaces by epithelial cell microvilli and cilia.Electron dense tracer particles (biological India ink, Thorotrast, ferritin) injected into the cerebral ventricles were ingested rapidly by epiplexus cells. Uptake of the particles was by way of coated surface invaginations which produced coated cytoplasmic microvesicles. Particle-containing microvesicles subsequently fused with each other and presumably also with pre-existent cytoplasmic vacuoles and lysosomal dense bodies to form storage vacuoles (phagosomes phagolysosomes and residual bodies).Present evidence suggests that epiplexus cells are of hematogenous origin. Under certain conditions these cells may detach from the surface of the choroid plexus to become free-floating cells in the various cerebrospinal fluid compartments of the brain.This investigation was supported by USPHS research grants 1-K04 HD20871, 5 R01 HD 02616 and NB-04456.     

The corpus luteum of the guinea pig. IV. Fine structure of macrophages during pregnancy and postpartum luteolysis, and the phagocytosis of luteal cells.

Little information is available on the ultrastructure of macrophages in the corpus luteum or their importance in the regression of luteal tissue. In the present study, the fine structure of activated luteal macrophages during pregnancy and the postpartum period was examined by electron microscopy of guinea pig ovaries fixed by vascular perfusion. In these corpora lutea, macrophages can readily be distinguished from luteal cells. Activated macrophages typically display three prominent inclusions in their cytoplasm: (1) heterophagic vacuoles, (2) distinctive large dense inclusions, and (3) large and small electron-lucent vacuoles. In addition, they contain numerous smaller lysosome-like dense bodies. Activated macrophages in corpora lutea also characteristically show many surface protrusions, such as processes, folds or pseudopodia, which often occur in close contact with nearby luteal cells. Generally, nuclei of macrophages are irregular in shape and display a dense border of heterochromatin, thus differing from those of luteal cells. Macrophages seem to be most abundant in regressing corpora lutea, where they commonly display heterophagic vacuoles containing recognizable luteal cell fragments, evidence that these phagocytes ingest senescent luteal cells. The digestion of luteal cell components in heterophagic vacuoles presumably gives rise to the distinctive large dense inclusions typically seen in macrophages. The findings of this study indicate that macrophages play a central role in luteolysis by phagocytizing luteal cells or their remnants. They therefore appear to bring about the reduction in volume of the corpus luteum that occurs as this tissue regresses. These results taken together with those previously published (Paavola, '78) further indicate that breakdown of the corpus luteum during postpartum luteolysis in guinea pigs involves both autophagy and heterophagy.     

Uptake of horseradish peroxidase from CSF into the choroid plexus of the rat,with special reference to transepithelial transport

Summary Protein uptake from cerebral ventricles into the epithelium of the choroid plexus, and transport across the epithelium were studied ultrastructurally in rats. Horseradish peroxidase (HRP, MW 40,000) was used as protein tracer. Steady-state ventriculo-cisternal perfusion with subatmospheric pressure (-10cm of water) in the ventricular system was applied. HRP dissolved in artificial CSF was perfused from the lateral ventricles to cisterna magna for various times, and ventriculo-cisternal perfusion, vascular perfusion or immersion fixation with a formaldehyde-glutaraldehyde solution was performed.Coated micropinocytic vesicles containing HRP were seen both connected with the apical, lateral and basal epithelial surface and within the cells. Heavily HRP-labeled vesicles were often fused with the lining membrane of slightly labeled or unlabeled intercellular spaces. Since the apical tight junctions of the epithelium never appeared open or never contained HRP in the spaces between the fusion points, and since the intercellular spaces between adjacent epithelial cells below the junctions only infrequently contained tracer after 5 min, by increasing amounts after 15–60 min of HRP perfusion, a vesicular transport of HRP from the apical epithelial surface to the intercellular spaces, bypassing the tight junctions, is suggested.In addition to the transepithelial transport, micropinocytic vesicles also transported HRP to the lysosomal apparatus of the epithelial cells. With increasing length of exposure to HRP, a sequence of HRP-labeled structures could be evaluated, from slightly labeled apical vacuoles and multivesicular bodies to very heavily labeled dense bodies.     

Studies of the mechanism of spleen cell cure for osteopetrosis in ia rats: appearance of osteoclasts with ruffled borders

After ia (osteopetrotic) rats receive whole body radiation and an injection of spleen cells from a normal littermate, the dense, sclerotic skeleton characteristic of osteopetrosis is rapidly remodeled and becomes normal in appearance radiographically and histologically within three weeks. The mechanism of this skeletal transformation has been explored in cured ia rats by light and electron microscopic examination of osteoclasts. In ia rats less than 25 days of age, osteoclasts viewed by electron microscopy lack a ruffled border - the extensive elaboration of plasma membrane next to the bone surface. Cured ia rats have osteoclasts with ruffled borders indistinguishable from those of normal littermates. In ia rats that receive only 600 rads whole body radiation, osteoclasts are still present three weeks later, but appear abnormal by light microscopy, with dense nuclei and lacking cytoplasmic vacuoles next to the bone surface. Cured ia rats have two types of osteoclasts, one type indistinguishable from osteoclasts of normal littermates by light microscopy, the other resembling osteoclasts of ia rats that received radiation only. These data indicate that the mechanism of the spleen cell cure for osteopetrosis in ia rats is rapid remodeling of the skeleton produced by osteoclasts with ruffled borders. Whether normal spleen cells produce these osteoclasts directly by cell division or indirectly by elaboration of some unknown local factor required for formations of ruffled borders by ia osteoclasts is not known.     

Cytodifferentiation and degeneration of odontoclasts in physiologic root resorption of kitten deciduous teeth

To investigate the cytodifferentiation and degeneration of odontoclasts in physiologic root resorption, we studied deciduous incisors undergoing resorption in 6-month-old kittens by electron microscopy of ultrathin sections. The endogenous peroxidase activity within the cells was also examined by incubating the tissue slices in diaminobenzidine-H2O2 medium. The resorbing tissues, consisting of multinucleated giant cells, macrophages, granular leukocytes, fibroblasts and many blood vessels, were observed at the resorbing surface of the root dentine. Macrophages and granular leukocytes exhibited endogenous peroxidase activity, but mononuclear and multinucleated preodontoclasts and multinucleated odontoclasts did not. These preodontoclasts contained abundant mitochondria, a moderate amount of rough endoplasmic reticulum, stacks of Golgi membranes, lysosomes and numerous polyribosomes scattered throughout the cytoplasm. Many cellular processes extended from their cell surfaces by which the preodontoclasts appeared to fuse to one another during their multinucleation. Concomitant with the multinucleation process, the preodontoclasts developed numerous pale vacuoles throughout the cytoplasm. These vacuoles seemed to arise from some smooth endoplasmic reticula, perhaps representing Golgi-endoplasmic reticulum-lysosome, and the Golgi saccules. However, the preodontoclasts did not yet form a ruffled border and clear zones. When these preodontoclasts came into direct contact with resorbing dentine surfaces, they began to form the clear zones against dentine surfaces. Characteristically, numerous pale vacuoles were accumulated in the cytoplasm adjacent to the clear zone, then they penetrated into the cytoplasm of the clear zone, and with this, ruffles of the plasma membranes appeared. Through a further movement of more pale vacuoles towards the ruffled plasma membranes, the odontoclasts developed typical ruffled borders against the resorbing dentine surfaces. At this differential phase, little pale vacuoles appeared in the Golgi area, but the cisterns of the Golgi apparatus themselves reached their greatest extent during cellular differentiation. Fully differentiated odontoclasts frequently extended long broad cellular processes into the dentinal tubules exposed to the resorption lacunae. Although some odontoclastic processes penetrating the dentinal tubules contained vacuoles and lysosomal structures, most processes lacked any cytoplasmic organelles, and their cytoplasm resembled that of the clear zone. But these processes never exhibited ruffled-border-like structures.(ABSTRACT TRUNCATED AT 400 WORDS)     

大白鼠第三脑室室管膜的超微结构

本文用扫描和透射电镜证实在成年大白鼠的第三脑室存在室管膜上神经元样细胞、神经胶质细胞和类组织细胞。神经纤维发自神经元样细胞或自脑室外穿入室腔而来,其末梢内含有清亮囊泡或兼有大颗粒囊泡。室腔內尚有膨大的树突末梢和室管膜细胞的球状小体。上述各种结构与感受、分泌和调节功能有关,并为下丘脑控制垂体机能的另一新途径(经脑脊液和室管膜)提供了形态学依据。     

Endocytotic pathways at the ruffled borders of rat maturation ameloblasts

Summary Using horseradish peroxidase (HRP) as a soluble protein tracer, electron microscopic studies were carried out in order to analyze endocytosis in the ruffle-ended ameloblasts of rat incisors. Accumulated HRP was initially incorporated from the ruffled border into the cytoplasm by means of pinocytotic vacuoles (pinosomes) and pinocytotic coated vesicles. The majority of the HRP was taken up by the large number of pinosomes, which then formed large endocytotic vacuoles by fusing either with each other or with preexisting endocytotic vacuoles. As time passed HRP accumulated, not in the pinosomes and ruffled border but in the endocytotic vacuoles and multivesicular bodies. Frequent connections between HRP-labeled coated vesicles and these cytoplasmic bodies indicate that these vesicles serve as an HRP carrier. These findings strongly suggest that ruffle-ended ameloblasts actively absorb soluble proteins from the enamel matrix during enamel maturation.     

Scanning and transmission electron microscopy of the subfornical organ of the grass frog (Rana pipiens)

Summary The ventricular surface of the subfornical organ of the frog is made up of ependymal cells with numerous apical microvilli, occasional cytoplasmic protrusions and many vacuoles projecting into the lumen of the third ventricle. Between these cells dendrites of cerebrospinal fluid-contacting neurons reach the ventricle to terminate in bulbous enlargements. In addition, flask-shaped encephalo-chromaffin cells, containing granulated vesicles and aggregates of filaments in their cytoplasm, project into the cerebrospinal fluid. Surrounding the centrally located capillaries are enlarged dendrites and axons of heterogeneous morphology, some of which appear to originate within the subfornical organ, intermingled with dendrites and axons of normal structure. The glial cells in this region, especially the microglial cells, often contain large lipofuscin inclusions, suggestive of degeneration and subsequent phagocytosis of some of the enlarged dendrites and axons. The normally scarce neurosecretory peptidergic axons become more evident and form typical Herring bodies in stalk-transected animals. Neuronal perikarya of varying morphology are predominantly located peripheral to the region of enlarged dendrites and axons. Supraependymal macrophages are particularly numerous on the subfornical organ.Abbreviations used CSF cerebrospinal fluid - SEM scanning electron microscope, scanning electron microscopy - SFO subfornical organ - TEM transmission electron microscope, transmission electron microscopy Supported, in part, by NIH grant NB 07492The skillful technical assistance of J.G. Linner and the secretarial assistance of Ann Gerdom are gratefully acknowledged. The SEM studies were made possible through a grant from the Graduate College of Iowa State University and the use of the SEM facility in the Department of Botany     

Endocytotic pathways at the ruffled borders of rat maturation ameloblasts

Using horseradish peroxidase (HRP) as a soluble protein tracer, electron microscopic studies were carried out in order to analyze endocytosis in the ruffle-ended ameloblasts of rat incisors. Accumulated HRP was initially incorporated from the ruffled border into the cytoplasm by means of pinocytic vacuoles ( pinosomes ) and pinocytotic coated vesicles. The majority of the HRP was taken up by the large number of pinosomes , which then formed large endocytotic vacuoles by fusing either with each other or with preexisting endocytotic vacuoles. As time passed HRP accumulated, not in the pinosomes and ruffled border but in the endocytotic vacuoles and multivesicular bodies. Frequent connections between HRP-labeled coated vesicles and these cytoplasmic bodies indicate that these vesicles serve as an HRP carrier. These findings strongly suggest that ruffle-ended ameloblasts actively absorb soluble proteins from the enamel matrix during enamel maturation.     

Decidual cells in the human ovary at term. I. Incidence, gross anatomy and ultrastructural features of merocrine secretion

Decidual tissue occurring within the human ovarian cortex was examined by light and electron microscopy. Of 21 ovarian specimens obtained at term (36-42 weeks of gestation), decidual cells were confirmed in each. Decidual cells were found within the tunica albuginea as single cells, in nodules, in polyps or in confluent sheets. Decidual cells exhibited several characteristics of cells engaged in secretory activity: abundant rough and smooth endoplasmic reticulum, numerous profiles of the Golgi complex and a large, euchromatic nucleus devoid of heterochromatin and displaying a prominent fibrous lamina. Peduncular protrusions at the periphery of the cell contained numerous dense bodies 0.4-0.9 micron in diameter. These dense bodies were bounded by a single membrane and contained granular subunits 30-60 nm in diameter. These granular subunits were observed in the process of apparent exocytosis, as well as free in the extracellular space. Secretory bodies and their granular content also were observed both in the region of the Golgi complex and partially extruded into peduncular processes. By far the greatest number of secretory bodies occurred within peduncular processes where they may be stored prior to release. Migration of a secretory body into a peduncular process and exocytosis from such a process appears to be an unusual mode of meocrine secretion, perhaps unique to decidual cells.     

Periodic organization of the contractile apparatus in smooth muscle revealed by the motion of dense bodies in single cells

To study the organization of the contractile apparatus in smooth muscle and its behavior during shortening, the movement of dense bodies in contracting saponin skinned, isolated cells was analyzed from digital images collected at fixed time intervals. These cells were optically lucent so that punctate structures, identified immunocytochemically as dense bodies, were visible in them with the phase contrast microscope. Methods were adapted and developed to track the bodies and to study their relative motion. Analysis of their tracks or trajectories indicated that the bodies did not move passively as cells shortened and that nearby bodies often had similar patterns of motion. Analysis of the relative motion of the bodies indicated that some bodies were structurally linked to one another or constrained so that the distance between them remained relatively constant during contraction. Such bodies tended to fall into laterally oriented, semirigid groups found at approximately 6-microns intervals along the cell axis. Other dense bodies moved rapidly toward one another axially during contraction. Such bodies were often members of separate semirigid groups. This suggests that the semirigid groups of dense bodies in smooth muscle cells may provide a framework for the attachment of the contractile structures to the cytoskeleton and the cell surface and indicates that smooth muscle may be more well-ordered than previously thought. The methods described here for the analysis of the motion of intracellular structures should be directly applicable to the study of motion in other cell types.     

Scanning electron microscopy of macrophages in the tail musculature of the metamorphosing anuran tadpole,Rana japonica

Summary Scanning electron microscopy was used to investigate the morphological changes of the tail musculature of the metamorphosing anuran tadpole, attention being focused on phagocytosis by macrophages. Muscle fibers were stained en bloc with silver and freeze-fractured during dehydration, or torn after drying. Samples were sputter-coated with gold-palladium and observed in both secondary electron- and back-scattered electron modes with a scanning electron microscope.Various cells were identified by the methods of secondary electron- and back-scattered electron images. Some macrophages lying between muscle fibers at prometamorphic stages possessed numerous finger-like projections and well-developed ruffles. During degeneration of muscle fibers macrophages collected in the degenerating region and invaded the space between the disordering myofibrils. In advanced stages the numbers of macrophages clearly increased on or around the degenerating muscle fibers. At the climactic stage fragmented muscles were entrapped and then engulfed by the macrophages. With the completion of phagocytosis, the macrophages became globular with reduction of the ridge-like ruffles. Macrophages may play a role not only in scavenging the fragmented muscle fibers, but also using their long processes in active formation of the fragments.     

Erythroid cells of the bone marrow of the mouse

The bone marrow of three intact male mice of C57Bl/6 line, fixed by perfusion of isotonic fixative of Karnovsky, has been studied by means of the scanning electron microscopy method. The surface of erythroid cells, that are immediately connected with macrophages of the erythroblasts islets, is analysed. According to the surface form, the erythroid cells are devided into 5 types. Every maturation stage of the erythroid cells is characterized by a certain type of surface. For identification of basophilic and polychromatophilic proerythrocytes the combined method of light and electron scanning microscopy of the cells in suspension is used. The bone marrow cells, obtained from the two male mice of C57Bl/6 line are fixed with the same fixative on special glasses with grids traced on them, stained after Romanovsky-Giemsa method and in moist preparations are examined in the light microscope. After further treatment the surface of the same cells in studied in the scanning electron microscope.     

Vascular permeability (problem of the blood-brain barrier) in the pineal organ of the rainbow trout,Salmo gairdneri

Summary The problem of the blood-brain barrier in the pineal organ of the rainbow trout, Salmo gairdneri, was investigated following intraperitoneal or intracardial injections of several tracers and dyes with different molecular weights. As demonstrated at the light-microscopic level, repeated injections of trypan blue or horseradish peroxidase (HRP) resulted in an accumulation of these substances in the pineal epithelium (parenchyma). By use of the electron microscope, HRP was found in electron-dense bodies, probably lysosomes, in (i) the endothelial cells and perivascular macrophages 4 h after intraperitoneal injection, (ii) the supporting cells and intrapineal or luminal macrophages 8 h after injection, and (iii) the receptor cells 24 h after injection of the tracer. Ferritin particles penetrated the fenestrated endothelium of pineal capillaries. They were confined to vesicles, vacuoles and the smooth endoplasmic reticulum of the supporting cells as well as to the synaptic vesicles and the smooth endoplasmic reticulum of the pineal photoreceptors. The intercellular passage of tannic acid mixed with the fixative was blocked at the luminal junctional complex separating the pineal lumen from the basal portion of the pineal epithelium. The passive intercellular transport of substances with high molecular weight from the bloodstream to the cerebrospinal-fluid compartment is thus prevented. However, no blood-brain barrier exists for exogenously administered proteins, which are rapidly taken up by pineal cells and actively transported in a transcellular manner.The findings on the blood-brain barrier of the pineal organ of the rainbow trout are discussed with particular reference to the endocrine capacity of pineal sensory organs.Fellow of the Alexander von Humboldt Foundation, Federal Republic of Germany.     

Fetal mouse lung in circumfusion system cultures.

Fetal mouse lungs were cultivated, using the dual-rotary circumfusion system for tissue culture, and their histotypic development was surveyed for 75 days by phase-contrast and electron microscopy. Alveoli, terminal bronchioles and alveolar macrophages were photographed periodically with still and time-lapse phase-contrast microscopy. Their histotypic appearance was confirmed by electron micrographs of the 1- and 2 1/2-month-old specimens. These revealed typical alveoli surrounded by a basal lamina and composed of types I and II pneumocytes containing various lamellar-body forms within the type II cells, the alveolar lumen, and the alveolar macrophages. There was a shift from almost all type II cells in the 1-month-old alveoli to the presence of frequent type I cells as constituents of the alveoli in the 2 1/2-month-old cultures. The terminal bronchioles were tubules consisting of ciliated cells with Clara cells interspersed between them. The ciliated cells contained as many as 30 cilia or basal bodies per section and numerous microvilli. They were attached to each other and to the Clara cells by junctional complexes and accessory desmosomes which were generally in the apical ends of the cells. The Clara cells typically had glycogen granules interspersed between lamellae of the endoplasmic reticulum, contained numerous well dispersed mitochondria, occasional lysosome-like granules and crystalloid bodies which appeared to be tubular. Some Clara cells presented a moderatley dense secretory granule in the center of the whorl of the endoplasmic reticulum.     

Potassium chloride-insoluble myofilaments in vertebrate smooth muscle cells

Actomyosin was extracted from avian gizzard smooth muscle. The residue was then homogenized and fractionated by differential centrifugation. Fractions of the residue that sedimented at 1 000 g and 13 000 g were examined in negatively stained and sectioned preparations with the electron microscope. The major components of both fractions were 100 Å diameter filaments and fusiform dense bodies. The filaments and dense bodies closely resembled their counterparts in sectioned preparations of unextracted smooth muscle cells from Taenia coli. The insolubility of the 100 Å diameter filaments at high ionic strength and their detailed structure suggest that they are not composed of actin and myosin. Their general features indicate that they correspond to the so-called thick filaments observed in the early studies of vertebrate smooth muscle cells.     

Smooth muscle-like cells in ovaries of the hamster and gerbil

Summary Smooth muscle-like cells are present in thecae externae, corpora lutea, and interstitial tissue of hamsters and gerbils. The smooth muscle-like cells, as examined by electron microscopy, are fusiform with central nuclei; the cytoplasm contains numerous myofilaments, dense bodies, micropinocytotic vesicles, and dense accumulations of glycogen-like particles. In addition to the smooth muscle-like cells, fibroblasts and cells that have characteristics of both fibroblasts and smooth muscle are located in the thecae externae of both species. There is no ultrastructural evidence of innervation in the theca folliculi, corpora lutea, or interstitial tissue of either species.A possible function for the smooth muscle-like cells is discussed.     

Scanning and transmission electron microscopy of the female reproductive system of Schistosoma margrebowiei Le Roux, 1933

Transmission electron microscopy shows that the uterus of female Schistosoma margrebowiei possesses the same ultrastructure as that of the tegument but lacks spines and sense organs. It does not possess secretory cells and opens at the gonopore which by scanning electron microscopy was seen to be composed of numerous leaf-like protrusions. The morphology of the ovary is comparable with that of other Digenea. Immature and mature ova possess cortically arranged granules and occur within the posterior zone of the ovary. Cilia and lamellae line the luminal surface of the oviduct and ootype, the lamellae running unidirectionally along the duct. Only a single type of secretory cell is seen within Mehlis' gland and this produces dense bodies which are associated with Goldi bodies. Narrow cytoplasmic channels supported by microtubules deliver these secretory bodies to the ootype. The vitelline duct is lined with cilia and lamellae and the vitelline gland contains four types of cells, S1, S2, S3 and S4. Calcareous corpuscles are found within mature S4 cells.     

Staurosporine-induced morphological changes in the rat osteoblasts.

Treatment of cultured rat osteoblasts with staurosporine caused a rapid outgrowth of long slender cellular processes and the formation of stellate cells. The number of stellate cells increased with higher concentrations of and longer incubation with staurosporine. Scanning electron microscopy (SEM) revealed that the smooth surface of control polygonal cells became ruffled with many long slender cellular processes, thus increasing the cell surface area. Transmission electron microscopy (TEM) of the stellate cells showed a rich accumulation of large lipid droplets in the cytoplasm. Some lipid droplets had coalesced under the cytoplasmic membrane. We suggest that staurosporine has an effect on the differentiation of cultured rat osteoblasts.     

Ultrastructure and cytochemistry of the tegument of Orthocoelium scoliocoelium and Paramphistomum cervi (Trematoda: Digenea)

The tegument of Orthocoelium scoliocoelium and Paramphistomum cervi was examined using histochemical techniques and electron microscopy. On the basis of the distribution of acid and alkaline phosphatase (E.C. 3.1.3.2, E.C. 3.1.3.1), non-specific esterase (E.C. 3.1.1.1), cholinesterase (E.C. 3.1.1.7) and succinate dehydrogenase (E.C. 1.3.99.1) at light microscope level two distinct regions were recognized, an outer and an inner zone. Electron microscopy revealed that the tegument comprises an outer surface syncytium underlain by a thick subsyncytial zone and musculature. Deeper still occur the nucleated "tegumental cells". The latter are in cytoplasmic continuity with the surface syncytium via vacuolated cytoplasmic trabeculae which traverse the muscle layers and the subsyncytial zone. Three types of tegumental cells each lacking mitochondria were observed. The T1 cells synthesize discoid and electron dense T1 bodies while T2 cells produce oval and electron lucent T2 bodies. The third type of tegumental cells apparently produce no secretory bodies and may represent an embryonic cell type. The surface syncytium contains T1 and T2 secretory bodies and is bounded apically by a plasma membrane invested externally by a fuzzy and filamentous glycocalyx. The surface syncytium lacks mitochondria and is traversed by infoldings of the basal plasma membrane. Beneath the surface syncytium the subsyncytial zone is largely comprised of fibrous interstitial material. This zone, which is particularly thick in the amphistomes, is traversed by trabeculae and extensions of underlying parenchymal cells which usually contain mitochondria and lysosomes. The subsyncytial zone overlies numerous circular and longitudinal muscle fibres. The absence of mitochondria and enzymes associated with active transport suggests that the amphistome tegument may be mainly specialized for protection of the worm against mechanical and chemical conditions prevailing in the rumen. Active uptake of nutrients is probably not a primary function.