Ultrastructure of the reticulate uterus and specific features of matrotrophy in three species of higher cestodes (Cestoda,Cyclophyllidea)

The ultrastructure of the reticular uterus has been analyzed in pregravid and gravid proglottids of cyclophillid cestodes dwelling in water (Alcataenia dominicana and A. larina) and in terrestrial hosts (Arostrilepis tenuicirrosa). Cells of the medullary parenchyma surrounding the uterus are filled with lipid inclusions in all species investigated. The hypertrophic development of small excretory ducts that surround the uterus, contact the uterine epithelium, and penetrate the diverticula is characteristic of Alcataenia dominicana and Arostrilepis tenuicirrosa. A comparative analysis of the results and the data available for other cestode species allow for the assumption that the reticulate structure of the uterus, lipid accumulation, and contacts between the uterine epithelium and the excretory ducts are morphological and functional adaptations that enable matrotrophy and the attainment of maximal fecundity by cyclophillid cestodes.     

Placental Type Interactions and Evolutionary Trends of Development of Uterus in Cestodes

In Proteocephalus thymalli and P. torulosus, a contact of the placental type in uterus was shown to be formed at two different levels. At the first level an interaction occurs between outgrowths of uterine epithelium and thin capsule of embryos closely adjacent to uterine wall. The next level is formation of contact between neighboring egg capsules, which allows distributing nutrients among fetuses present in the uterine cavity. Placental interactions in Clestobothrium acheilognathi are limited in time and space. First, a relatively small number of eggs are involved in interaction of the placental type in the uterine sac, while uterine duct is filled with freely lying eggs. Second, the closest contact is observed in eggs with non-sclerosed egg shell. One of the main evolutionary tendencies in cestodes has been shown to be a modification of uterus for formation of close interrelations with embryonic membranes in the course of transition from the extrauterine to the intrauterine type of embryonic development. Uterus in parasites with a polylecital type of the egg is suggested to serve to the greater extent as a reservoir, whereas in cestodes with oligolecital eggs, uterus performs its direct function—supply of developing embryos with nutrients. As a result, modifications of uterine epithelium are formed: from the appearance of the placental type interactions formed repeatedly in phylogenetically distant groups of cestodes to formation of branched outgrowths separating the uterine space into units or disintegration to actively functioning uterine capsules.     

Morphology and ultrastructure of reproductive organs of <Emphasis Type="Italic">Monocercus arionis</Emphasis> (Sibold, 1850) Villot, 1982 (Cestoda: Cyclophyllidea)

The morphology of the reproductive system at different stages of ontogenesis and ultrastructural peculiarities of the copulatory organs and uterine in Monocercus arionis (Sibold, 1850) Villot, 1982 (Cyclophyllidea) have been studied. The muscle of the outer wall of the cirrus bag has a higher organizational level than typical smooth-muscle cells in cestodes. The cirrus is armed with typical filamentous and bladelike microtriches. The uterine epithelium contacts the thin capsule of the developing embryos located closely to the uterus wall, and the embryos contact each other in the uterine cavity in what can be interpreted as placental interactions. The specificity of the structure and arming of the copulatory apparatus has been considered, and the ultrastructural peculiarities of the uterus in the members of different orders of cestodes have been compared and analyzed.     

Morphology and ultrastructure of the uterus of Lineolepis scutigera (Dujardin, 1845) Karpenko, 1985 (Cestoda,Cyclophyllidea, Hymenolepididae) in formation of uterine capsules

The microanatomy and ultrastructure of the uterus in different stages of ontogenesis were studied in a cyclophyllidean cestode Lineolepis scutigera. In the early stages, developing embryos lie freely in the cavity of a single unbroken uterus, which is later fragmented into separate compartments. As a result, numerous spherical uterine capsules are formed; each of them contains one formed egg. Capsules represent a fragmented but actively functioning uterus. Muscular cells containing numerous lipid inclusions are located around them. In the final stages, placenta-like relationships are formed between eggs and the epithelium of capsules. A comparative morphofunctional analysis of uterine capsules in cestodes is presented. Attention is paid to the formation of close interactions between the uterine epithelium and developing eggs.     

Ultrastructure of genital system ducts of Diphyllobothrium latum (Cestoda:Pseudophyllidae): the ducts of the female reproductive system

The components of the female reproductive system of Diphyllobothrium latum, including ovary, ovicapt, oviduct, vitelline ducts, vitelline reservoir, vagina, seminal receptacle, ootype with unicellular Mehlis's gland, ootype-uterine duct and uterus were observed with the electron microscope. The epithelium of the female reproductive system ducts consists of a nucleate syncytial layer. Structural differences in apical surface of the ducts, the number of nuclei and organoids in syncytial layer as well as the number of underlaid muscles were revealed. The regional differentiations of the uterus wall were registered. The middle and distal region of uterus was covered with microtriches. The filamentous microtriches were observed in apical surface of vagina. The epithelium of seminal receptacle and distal region of uterus were underlaided by the powerful muscle layers. The fertilization canal was revealed. It was shown that the formation of egg shells implemented by the deposit of vitelline globules in their surface in the ootype-uterine duct. Structural and functional differences of different parts of female apparatus in various groups of cestodes are conditioned by species biology.     

Structure of Reproductive System of the Amphicotyllide Cestode Eubothrium rugosum (Cestoda, Pseudophyllidae)

A tendency for increase both of numerical and of ecological factors of infestation in pseudophyllid cestodes is realized due to morphological peculiarities of the structure of their reproductive system. In the species E. rugosum with the closed bursiform uterus and intrauterine development of eggs, there are revealed the same degree of maturity of oocytes in ovary, the lack of sphincter or filtering cell at the base of the ovicapt infundibulum, and the presence of a large vitelline reservoir. By analogy with trematodes, an interconnection is traced between the degree of egg maturation in the uterus and morphology of uterus and vittelicles. The thickening of the egg membrane has been shown to occur not only by deposits of individual vitelline globules at the internal superficial egg layer, but also by binding of lipid droplets excreted from the surrounding parenchyma to the uterine tube along its entire length to the external egg surface. The male reproductive system of Eubothrium rugosum is characterized by the presence of a small cirrus pouch, by the cirrus supplied with microtrichia, which corresponds to the similar vagina structure, and by localization of prostate glands outside the cirrus pouch. Comparison is presented with other ultrastructural peculiarities of organization of the reproductive system in the earlier studied species of pseudophyllid cestodes, Diphyllobothrium latum.     

Ultrastructure of nephridial systems in cyclophyllidean cestoda: Catenotaenia pusilla (Goeze, 1782), Hymenolepis diminuta (Rudolphi, 1819) and Inermicapsifer madagascariensis (Davaine, 1870) Baer, 1956]

Electron microscopic study of nephridial systems in three cyclophyllidean cestodes indicates a resemblance in their ultrastructure. The walls of longitudinal, transverse and collecting ducts show a very similar pattern of organization. The surface of the anucleate epithelium lining the ducts is developed into microvilli. A relatively thick layer of fibrillar tissue underlies the basal membrane of the microvillar epithelium. The nucleated portions or "pericaryons", situated between the parenchymal cells, are directly connected with epithelium by cytoplasmic prolongations. The canalicular lumen extends through a single series of cells curved into a ring. The epithelial surface of the canalicular wall is developed into short, densly staining microvilli and the immediately underlying fibrillar tissue appears very compact. The cilia were never observed in any of the above ducts. The ultrastructure of protonephridia proper is comparable with those already described in other cestodes. There is a close association between the flame-cell and the cancalicular ending, enlarged into a nephridial funnel. A single row of nephridial rods of the flame-cell is surrounded by a row of digitiform prolongations of the nephridial funnel border. The prolongations alternate with the rods and their interlocking pattern appears clearly in cross-sections. A series of minute pores or "nephrostomes" providing a direct contact between the nephridial chamber and intercellular space of the paranchyma was shown. The problem of classification and definition between the "closed" protonephridia and open metanephridia is discussed. The structural unity of protonephridia in different groupes of Platyhelminthes is reviewed. The different number of flagella within the "flames" of different cestodes is compared and analyzed. The ultrastructural characteristics of duct-wall epithelium provides some confirmation of its high metabolic activity.     

Extraordinary case of matrotrophy in the African skink Eumecia anchietae

The viviparous African skink, Eumecia anchietae, exhibits a matrotrophic fetal nutritional pattern. Until well after the limb bud stage, extravitelline nutritional provision is in the form of holocrine secretion originating from the stratified uterine epithelium of the uterine incubation chambers. Uterine secretions are absorbed by a specialized yolk sac ectoderm and chorioallantois through histotrophy. The yolk sac is not in close contact with the uterine lining from the limb bud stage onwards. The yolk sac ectoderm forms invaginations filled with uterine secretion and consists of a single layer of vacuolated hypertrophied cells bearing microvilli. The chorioallantois at the limb bud stage is extensive, well-vascularized, and not intimately associated with the uterine epithelium. Where the uterus is folded, the chorioallantois may interdigitate loosely. Chorionic cells are low to high columnar, clearly vacuolated, and bear microvilli. The allantoic layer consists primarily of squamous cells exhibiting villous projections. By the time embryos have well-defined digits, the specialized yolk sac ectoderm has regressed and the yolk sac lumen has been invaded by vitelline cells. The chorioallantois is very extensive and in areas greatly folded. Where it contacts the uterine epithelium, a proper chorioallantoic placenta is formed. Cell layers of the chorioallantois and uterine epithelium are thin and cuboidal to squamous in appearance. The chorioallantoic placenta is simple in structure, occurs throughout the incubation chamber, and is epitheliochorial in arrangement. It is unknown whether the placentome observed in other highly matrotrophic scincids is formed in late stage embryos of this species.     

The germ layer origin of mouse vaginal epithelium restricts its responsiveness to mesenchymal inductors: uterine induction

The epithelium of the mammalian vagina arises from two distinct germ layers, endoderm from the urogenital sinus and mesoderm from the lower fused Müllerian ducts. While previously it has been reported that neonatal vaginal epithelium can be induced to differentiate as uterus, which normally develops from the middle portion of the Müllerian ducts, it has not been determined whether this ability is shared by both mesoderm- and endoderm-derived vaginal epithelia. To test if germ layer origin influences the ability of vaginal epithelium to undergo uterine differentiation, we have isolated sinus-derived and Müllerian-derived vaginal epithelia from newborn mice, combined them with uterine mesenchyme, and grown them for 4 weeks in female mice. Mesoderm-derived Müllerian vaginal epithelium in combination with uterine mesenchyme formed the simple columnar epithelium typical of uterus. Similar results were obtained with neonatal cervical epithelium, another mesodermal Müllerian duct derivative. On the other hand, sinus vaginal epithelium combined with uterine mesenchyme formed small cysts lined by a stratified squamous vaginal-like epithelium. This epithelium never showed evidence of cycling between the cornified and mucified states as is typically seen in vaginal epithelium combined with vaginal stroma. These results indicate that the ability of epithelium to form uterus is limited to mesoderm-derived epithelia and suggest that endoderm-derived sinus vaginal epithelium cannot undergo the typical differentiative modifications in response to the hormonal fluctuations of the estrous cycle when associated with uterine stroma.     

Immunohistochemical localization of estrogen receptor-α in sex ducts and gonads of newborn piglets

Estrogen receptor-alpha (ER-alpha) expression in piglet uteri has previously been reported from day 15 after birth. Nevertheless, uterine tissue has been reported to be estrogen sensitive from the day of birth. Since estrogen action in the uterine tissue is suggested to be mediated principally by ER-alpha, the present study aimed to evaluate the presence of ER-alpha in uteri of 1- to 2-day-old piglets by means of immunohistochemistry. In addition, sex ducts and gonads of both sexes were examined. The results clearly demonstrate the presence of ER-alpha immunopositive cells in uterine tissue, which explains its estrogen responsiveness. Immunostaining was most intense in the glandular epithelial cells and is suggested to indicate participation of ER-alpha in adenogenesis. In oviducts, almost all epithelial cells were immunostained moderately positive, while the stroma cells were stained comparably more positive. The functional significance of this intensity difference is uncertain but could indicate that part of the estrogen action on the epithelium is mediated through the stroma cells, as is known for the uterus. In ovaries, the surface epithelium and stroma cells were immunostained, whereas germ and granulosa cells were immunonegative. It is speculated that ER-alpha might be involved in yet unknown intraovarian mechanisms. In male sex ducts, immunostaining was virtually confined to the epithelium of efferent ducts. All cells in the epididymis as well as in vas deferens were immunonegative. The unique presence of ER-alpha in efferent ducts corresponds with localization in other species, where it has been shown to be involved in fluid reabsorption. The obtained data on localization of ER-alpha correspond with the present knowledge, obtained in ER-alpha knockout mice, of the biological function of ER-alpha within male and female gonads and sex ducts.     

Fine structure of the cirrus sac and vagina of progenetic Diplocotyle olrikii (Cestoda: Spathebothriidea)

Ultrastructural characteristics of the cirrus sac and vagina of progenetic and monoxenic spathebothriidean tapeworm, Diplocotyle olrikii from the body cavity of Gammarus oceanicus are described. Five loosely arranged muscle layers make up the cirrus sac wall. The nucleated syncytial cytoplasm of the ejaculatory duct's wall has apical lamellae and 3 well-developed muscular layers under epithelim. Numerous prostate ducts pass through syncytial epithelium of it. The numerous prostate glands are localized around cirrus sac. Unique morphology of the prostate granules with an electron-dense core surrounded by a matrix of lower density is revealed for the spathebothriidean tapeworms. The epithelial lining of the cirrus in D. olrikii is nucleated and also is connected to subsurface sunken perikarya. The apical surface of the cirrus is covered with small cone-shaped microtriches. Well-developed 10 closely arranged muscle layers support the cirrus. Three regions of the vagina are distinguished. The distal part of vagina has filamentous microthrix type on the surface similar to tegumental one, as well as middle and proximal regions are covered with small cone-shaped microtriches, reducing in their number to proximal part. Anucleate epithelial lining of vagina is connected to numerous sunken parikarya. The cirrus and vagina epithelial lining has numerous vesicles. A comparison is made of the fine structure of the cirrus sac and vagina of monoxenic and dixenic spathebothriidean species. Ultrastructural data on the cirrus sac and vagina of the Spathebothriidea are compared with those for monozoic and polyzoic cestodes. The ultrastructural spathebothriidean features are discussed.     

Viviparity and the maternal-embryonic relationship in the coelacanth Latimeria chalumnae

Synopsis Embryos of Latimeria chalumnae develop in well-vascularized compartments in the uterine region of the right oviduct. Compartments conform to the shape of their embryos and yolksacs; they represent a stable, gestation-induced oviductal modification. Late-term pups possess large, flaccid, vascular yolksacs almost devoid of yolk. The sac is in close contact with, but does not adhere to, the lumenal uterine surface. A massive vascular plexus occurs in the wall of the compartment at the site of contact with the yolksac; together they constitute a non-adherent, transposable placenta. The exterior surface of the yolksac is bounded by an attenuated, single-layered, squamous epithelium that surrounds an intercommunicating bed of cortical sinuses. The cortex of the sac is composed mostly of connective tissue stroma. The inner surface is bounded by a layer of yolk-digesting merocytes. Residual yolk occurs as yolk platelets that include yolk crystals. The interior surface of the sac is invested by an uniquely specialized vitelline circulation; no connection seems to exist between the interior of the yolksac and gut. The uterine wall consists of: (1) a lumenal surface composed of an anastomosing network of capillaries with a layer of attenuated, very thin, squamous epithelium, (2) a well-vascularized connective tissue stroma, (3) alternating transverse and longitudinal layers of smooth muscle, also well-vascularized, and (4) an external epithelial layer. Comparison of egg dry weight (184 g) with the estimated dry weights of a late-term pup (171 to 239 g) and a neonate (200 to 280 g) reveals a weight change of – 7 to + 30% and + 9 to + 52%, respectively. This is indicative of matrotrophy. In one female specimen, 19 remarkably large ovulated eggs were found and in another about 30 somewhat smaller ovarian ones. These are many more than ever could be accommodated in the uterine space. During the early and middle phases of development, embryos must be lecithotrophic, using their yolk reserves, with oophagy of fragmented supernumerary eggs as the most probable source of additional nutrients. The well-developed embryonic gut contains brown, amorphous yolk-like material. The limited amount of metachromatic secretory product of the uterine glands can play little or no role in embryonic nutrition.     

Observations on the morphology of Toxocara pteropodis eggs

Fertile eggs of Toxocara pteropodis, passed in the faeces of juvenile flying-foxes, were ovoid to spheroid in shape with a diameter range of 80-110 microns. The shell was often seen to comprise 4 layers: a fine inner lipid layer, a thicker clear chitinous layer, an equally thick outer vitelline layer and a pitted outermost, proteinaceous uterine layer of variable thickness. Infertile eggs were less uniform in shape and generally did not have well-defined shell layers, the formation of which is triggered by sperm penetration of the oocyte. The eggs of this species are bulkier than those of related ascaridoids, apparently because of a thicker external coat which, while not providing mechanical strength, is thought to protect against desiccation. Scanning electron microscopical findings suggest that the outer layer is not applied directly by uterine cells, but forms by the gradual deposition of secretions in the uterine lumen, regardless of whether the oocyte has been fertilized.     

Structure of the epithelium in the large milk ducts and milk sinuses of the bovine udder

The two-layered epithelium of the large milk ducts and the milk sinus of the bovine udder were studied by light and electron microscopy. Whereas the cells of the basal cell layer are poor in cell organelles, the cells of the apical layer shows many cell organelles and microvilli at the surface. This hints at processes of reabsorption through the apical cell layer. Together with the fast junctional complex between the cells, this confirmes the function of the epithelium as a barrier within the local defense system of the bovine udder.     

Oogenesis and egg-shell formation in Aspiculuris tetraptera Schulz (Nematoda: Oxyuroidea).

The ovary of Aspiculuris tetraptera has a prominent terminal cap cell. This is considered to be part of the ovarian epithelium. Oogonia detach from the short rachis and increase in size from 6 to 60 microns; accumulating hyaline granules, shell granules and glycogen. The hyaline granules persist in the eff cytoplasm after shell formation has been completed and are considered to be lipoprotein yolk. The shell granules contribute to the non-chitin fraction of the chitinous layer. A classification of the cytoplasmic inclusions of the nematode oocyte is proposed. Upon fertilization a vitelline membrane is formed which constitutes the vitelline layer of the egg-shell. The chitinous layer is secreted in the perivitelline space, between the vitelline layer and the egg oolemma. Upon completion of chitinous layer synthesis, the egg cytoplasm contracts away from its inner surface. The material of the lipid layer is secreted at the surface of the egg cytoplasm and adheres to the inner surface of the chitinous layer. During secretion of the chitinous and lipid layers by the egg cytoplasm, the uterine cells secrete the unit membrane-like external uterine layer and the crystalline internal uterine layer. A complex system of interconnecting spaces develops in the internal uterine layer. This system is open to the exterior via breaks in the external uterine layer. There is no direct involvement of the uterine cells in the formation of this structure.     

The fine structure of frontal glands in adult cestodes

Kuperman B. I. & Davydov V. G. 1982. The fine structure of frontal glands in adult cestodes. International Journal for Parasitology12: 285–293. The localization and structure of frontal glands of adult cestodes of 20 species from 4 orders: Caryophyllidea, Pseudophyllidea, Proteocephalidea and Cyclophyllidea were studied by light and electron microscopy. In cestodes of various orders there was evidence of differences in the ultrastructure of secretory cells, in the character of the secretion, and in the method of its discharge. The localization of glands in most adult cestodes is in the scolex. In Cyatocephalus, Ligulidae, Bothriocephalus claviceps, they are distributed also in the anterior and middle part of the body. In the species Caryophylleus (C. laticeps) and Khawia sinensis a major gland complex previously not described was discovered. The glands of the cestodes investigated may be divided into three main groups by their structure, localization and functional role in ontogenesis: (1) penetration glands in oncospheres which develop into procercoids and plerocercoids; (2) glands of plerocercoids and adult cestodes which develop in the gut; (3) gland complexes in the representatives of the order Caryophyllidea. The secretion is usually discharged at the scolex region and less frequently on the lateral surface. Three different ways of discharging secretory material from the cestodes body are described.     

The ultrastructure of the duct system in the rat extraorbital lacrimal gland

Summary The duct system of the rat exorbital lacrimal gland consists of intercalated ducts, interlobular ducts and excretory ducts. The morphological changes from one type of duct to the next are gradual. At the light microscopical level this consists of a change from a bilaminar epithelium in the intercalated ducts to an epithelium, consisting of approximately three layers — which may be pseudostratified — in the excretory ducts. The basal layer of the intercalated ducts consists of myoepithelial cells, whereas the inner epithelial cells may have both a secretory and an electrolyte transporting function. The interlobular duct epithelium contains many cells with deep infoldings of the basolateral plasma membranes and associated mitochondria, suggesting a similar function to the striated duct epithelium in salivary glands. Numerous basal cells in this epithelium have tentatively been interpreted as unusual myoepithelial cells. Nerve terminals have been observed in the ductal epithelium.This work was supported by the National Health and Medical Research Council of Australia. — We wish to thank Mrs. Eva Vasak for her expert technical assistance.     

Fine structure of the eggshells of four primitive moths: Hepialus hecta (L.),Wiseana umbraculata (Guénée) (Hepialidae), Mnesarchaea fusilella walker and M. Acuta philp. (Mnesarchaeidae) (Lepidoptera,Exoporia)

The eggshells of Hepialus hecta, Wiseana umbraculata (Hepialidae) and of Mnesarchaea fusilella (Mnesarchaeidae) (Lepidoptera, Exoporia) were studied by scanning electron microscopy (SEM) and transmission (TEM) electron microscopy. All 3 species show a very similar surface sculpture of the micropylar region which, however, is very different from the eggs of the Ditrysia. The micropylar plate is large and oval. There are only 2 or 3 micropylar openings. In the hepialid moths, the surface of the egg's main body is characterized by spherical protuberances. The radial fine structure of the eggshells of all 3 species as well as of alcohol-stored eggs of Mnesarchaea acuta (Mnesarchaeidae) is basically identical to the eggshell of Korscheltellus lupulinus (Hepialidae). The chorion consists of only one layer, which, in the hepialid species, shows a crystalline-like fine structure. The vitelline envelope is composed of a thin, laminated, outer layer (V-2) and a thick, rigid, inner layer (V-1) that is traversed by large numbers of canals. This kind of eggshell architecture is distinctively different from that of the ditrysian Lepidoptera.     

Specializations of the chorioallantoic placenta in the Brazilian scincid lizard,Mabuya heathi: a new placental morphotype for reptiles

New World skinks of the genus Mabuya exhibit a unique form of viviparity that involves ovulation of tiny (1 mm) eggs and provision of virtually all of the nutrients for embryonic development by placental means. Studies of the Brazilian species M. heathi reveal that the chorioallantoic placenta is unlike those reported in any other squamate genus and exhibits striking specializations for maternal-fetal nutrient transfer. The uterine lining is intimately apposed to the chorioallantois, with no trace of an intervening shell membrane or of epithelial erosion; thus, the placenta is epitheliochorial. The uterus exhibits multicellular glands that secrete organic material into the uterine lumen. Opposite the openings of these glands, the chorion develops areolae, invaginated pits that are lined by absorptive, columnar epithelium. A single, mesometrial placentome develops, formed by radially oriented uterine folds that project into a deep invagination of the chorion. Uterine epithelium of the placentome appears to be syncytial and secretory and overlies a rich vascular supply. The apposed chorionic epithelium is absorptive in morphology and contains giant binucleated cells that bear microvilli. Several specializations of the placental membranes of M. heathi are found among eutherian mammals, signifying evolutionary convergence that extends to histological and cytological levels. The chorioallantoic placenta of M. heathi and its relatives warrants recognition as a new morphotype for reptiles, defined here as the "Type IV" placenta. This is the first new type of chorioallantoic placenta to be defined formally for reptiles in over half a century.     

Implantation-induced changes in uterine arylamidase localization in the rabbit, rat, hamster and guinea-pig

Localization of uterine arylamidase activity varied between species: arylamidase was found primarily in the apical aspect of uterine epithelial cells in the rabbit, hamster and non-pregnant rat; only moderate staining was observed in these animals in the endometrial stroma. By contrast, arylamidase localization was primarily stromal in the guinea-pig at all stages studied while the luminal epithelium was devoid of reactivity. In all species, uterine enzyme activity increased before implantation but decreased in the vicinity of the blastocyst once implantation had begun. A generalized increase over the entire length of the uterus was seen during the preimplantation phase in the uterine epithelium of the rabbit and in the endometrial stroma of the guinea-pig. Increase in stromal activity appeared to indicate predecidual transformations which were embryo-dependent (i.e. localized to the implantation site) in the rat, or embryo-independent (i.e. occurring throughout the uterus) in the guinea-pig. A subsequent decrease in enzyme activity occurred in the vicinity of the implanting embryo irrespective of the cell type involved (epithelium in the rabbit, stroma/decidua in the rat and guinea-pig). Since arylamidases of the type studied here are integrated membrane proteins, the uniformity of changes observed in different species may reflect profound changes in membrane properties of endometrial cells as an element of the implantation reaction.