Hermaphroditic Duct Research Articles

The structure of the bursa copulatrix in virgin and mated snails, Helisoma duryi (Mollusca): role of acid phosphatase in reproduction

Abstract. The fine structure of the bursa copulatrix of the virgin snails has been compared with that of mated snails. One of the noticeable changes after mating is an increase in the number of the Golgi and the secretory vesicles. Since some of the vesicles react positively for acid phosphatase it is suggested that this enzyme activity increases following mating. The bursa lumen of the virgin snail contains gel‐like materials devoid of spermatozoa, however, following mating, the lumen is full of semen containing live spermatozoa and bacteria. The source of bacteria in the lumen is not known. Acid phosphatase activity is significantly higher in the luminal content of mated snails than in the virgin snails. The activity is higher in the lumen than in the epithelial cells, suggesting that the enzyme is secreted into the lumen where it is utilized for extracellular degradation of spermatozoa. Following mating, the spermatozoa are motile in the lumen of the bursa for ∼3–7 d, but become immobile and finally undergo extracellular digestion so that intact spermatozoa are not recognizable by day 10. The use of castrated snails in mating experiments suggest that individuals of Helisoma duryi reproduce by cross fertilization and that the bursa may act as the holding organ from where the spermatozoa are periodically transported to the carrefour over ∼7 d. At day 10 following mating, however, autosperms appear in the hermaphroditic duct awaiting the next mating.

The spermathecal epithelium, sperm and their interactions in the hermaphroditic land snail Arianta arbustorum (Pulmonata, Stylommatophora)

Previous investigations showed that in Arianta arbustorum incoming sperm are not equally distributed among all tubules of the sperm storage organ, the spermatheca, and it has been assumed that the sperm recipient might influence paternity after multiple mating. Understanding postmating sexual selection requires understanding the function of the genitalia. Against this background we analyse the ultrastructure of the spermathecal epithelium, give a brief description of the sperm morphology and describe the sperm–epithelium interactions. The epithelium of the spermatheca, which consists of up to nine blind tubules originating from a common duct, is a monolayer composed of a single cell type. Only the density of the ciliation increases along the tubules and the common duct. In addition, the cilia of the latter are more than 50% longer than those in the tubules. These long and densely arranged cilia not only prevent autosperm from getting into the spermatheca, but may also be responsible for sorting sperm in the spermatheca allowing the recipient to store sperm from different partners separately. The most peculiar characteristics of the epithelium are the wide intercellular spaces at the base continuing apically into narrow channels used for extracellular transport. Below apical junctions, the cells adhere to each other through interdigitations, which form an extensive labyrinth at the base and rest on the basement membrane. Rough endoplasmic reticulum and Golgi complexes are mainly found in the vicinity of the basally positioned nucleus. A large vacuole lies above the nucleus and the apical portion of the cytoplasm is densely populated with mitochondria. Vesicles of various sizes are also found mainly in the apical region. The spermatozoa stored in the hermaphrodite duct prior to transfer are characterised by an acrosome forming an angle of 90° with the longitudinal axis of the nucleus and vesicles of undefined shape in the terminal end of the flagellum. In the spermatheca the spermatozoa lose their perinuclear sheath and the acrosome is almost in line with the longitudinal axis of the sperm. This process is interpreted as capacitation. In the spermatheca, the capacitated spermatozoa are in close contact with the epithelial cells. However, an exchange of substances was not observed. It is assumed that the epithelium provides the environment for sperm quiescence rather than nutritives.

Life-cycle and biology of Sychnocotyle kholo n.g., n. sp. (Trematoda : Aspidogastrea) in Emydura macquarii (Pleurodira : Chelidae) from southern Queensland, Australia.

Sychnocotyle kholo n. g., n. sp. (Aspidogastrea: Aspidogastridae) is described from the small intestine of the freshwater turtle Emydura macquarii (Pleurodira: Chelidae). The new genus is distinguished from other aspidogastrids by the possession of the following suite of characters: no cirrus-sac; no hermaphroditic duct; four rows of alveoli on the ventral disc but no prominent papillae; Laurer's canal opening to the exterior. Eggs hatched to cotylocidia within 37-41 days at 17-24 degrees C. The life-cycle is obligate two-host, involving a mollusc and a freshwater turtle. Juvenile forms, almost entirely single worm infections, were found in the molluscs Corbiculina sp. (Bivalvia: Corbiculidae) and Thiara balonnensis (Prosobranchia: Thiaridae). Sychnocotyle is most likely to have evolved in Australia after the separation of Gondwanaland from Laurasia 120- 100 mya.

The functional organization of the carrefour in the reproductive tract of Biomphalaria tenagophila (Mollusca, Planorbidae)

Summary A detailed morphological analysis of the carrefour, corresponding to the site of bifurcation of the hermaphroditic duct of the reproductive tract of Biomphalaria tenagophila (Mollusca, Planorbidae), has been carried out by light and electron microscopy, including 3D anatomical reconstruction. The carrefour receives the tangential entrance of the ovispermiduct and secretory duct of the albumen gland in its posterior face whereas the exits to the oviduct and spermiduct are situated in its anterior face. Histologically, this bulbuous organ is very similar to the ovispermiduct and thus may be considered as a hermaphroditic structure. It is lined by highly ciliated columnar epithelium with a few mucous secretory cells. The he structural analysis of the epithelium reveals the presence of long and abundant cilia and numerous microvilli in the apical surface of the ciliated cells, along with signs of micropinocytic activity. The observation of basal membrane infoldings with associated mitochondria indicates the existence of an apex-base motion of fluid through the carrefour epithelium. In contrast, the mucous cells show an intense secretory activity. Germ cell trafficking and sorting inside the carrefour are very complex, involving the segregation of oocytes and spermatozoa produced in the ovotestis of the animal itself and the exogenous spermatozoa acquired by copulation. Based on morphological evidence presented in this work, we concluded that the flux produced by ciliary beating of the epithelial cells along with the insertion angle and relative positioning of the openings of the ducts in the carrefour are the most important factors in the traffic and differential destiny of the germ cells inside the organ. The presence of secretion of the albumen gland in the so-called fertilization pocket should prevent the sperm entrance into the oocyte and thus the zygote formation in this specialized region of the carrefour.

Pheromones linked to sexual behaviors excite the appetitive phase of feeding behavior of Aplysia fasciata II. Excitation of C-PR, a neuron involved in the generation of appetitive behaviors

Pheromones presumably released by conspecifics amplify both the appetitive and the consummatory components of feeding in Aplysia. These effects can be mimicked by administering homogenate of the large hermaphroditic duct containing atrial gland tissue, as well as peptides from the bag cells. Identified cerebro-pedal regulator (C-PR) neuron is thought to command various behaviors that comprise the appetitive phase of feeding. In a reduced preparation, we investigated the effects on the C-PR of applying these substances to the rhinophores, the sensory organs which detect pheromones. Stimuli that excite feeding in the animal were also found to affect the C-PR. Large hermaphroditic duct homogenate caused a doubling in the firing rate of the C-PR, and amplified the response of the C-PR to other excitatory stimuli, such as touch of food to the rhinophores. Bag cell peptides (α, β and γ bag cell peptide, and egg-laying hormone) caused smaller increases in the firing rate of the C-PR. These data are consistent with the hypothesis that pheromones facilitate appetitive feeding behavior in part via their excitation of C-PR.

Machidatrema n. gen. (Digenea: Hemiuridae: Bunocotylinae) and Phylogenetic Analysis of Its Species

Machidatrema n. gen. is proposed to include Neotheletrum frontilatum (Manter, 1969) Gibson and Bray, 1979, Neotheletrum akeh Machida, 1989, Genolinea kyphosi Yamaguti, 1970, and Genolinea chilostoma Machida, 1980. The new genus is characterized by the presence of strong muscles in the anterior part of the body, the hermaphroditic duct divided into 2 sections, prostatic vesicle, and excretory pore in a midventral position. Phylogenetic analysis of the 4 species, based on 14 characters, produced 1 most parsimonious tree with a consistency index of 0.938. The tree suggests that Machidatrema frontilatum and Machidatrema akeh are sister species; Machidatrema kyphosi is the sister species of the former 2, and Machidatrema chilostoma is the sister species of them all. The genus appears to have originated in the Pacific Ocean, parasitizing fishes belonging to Kyphosus; the common ancestor of M. frontilatum and M. akeh appears to have originated by a host-switching event to fishes belonging to Siganus, and M. frontilatum originated by allopatric speciation involving dispersal to the Indo-Pacific and Australia.

Molecular cloning of a cDNA encoding the neuropeptides APGWamide and cerebral peptide 1: localization of APGWamide-like immunoreactivity in the central nervous system and male reproductive organs of Aplysia.

While much is known about the neural and endocrine mechanisms that control egg laying in the gastropod mollusk Aplysia, relatively little is known about the regulation of male reproductive activity in this simultaneous hermaphrodite. In the present study, we have cloned and sequenced a cDNA that encodes a precursor protein, the predicted posttranslational processing of which presumably generates nine copies of the neuropeptide Ala-Pro-Gly-Trp-NH2 (APGWamide), five connecting peptide sequences, and a C-terminal peptide. The sequence of one connecting peptide is identical to the previously characterized cerebral peptide 1. Northern blot analysis identified two major APGWamide mRNA transcripts (approximately 1.3 kb, approximately 2.4 kb), which were present in central nervous system ganglia, but were most abundant in the right cerebral and right pedal ganglia. Immunohistochemical studies using sexually mature Aplysia demonstrated that the vast majority of APGWamide-like immunoreactivity was localized in 30-40 neurons along the anterior and medial margins of the right cerebral ganglion and in a cluster of 15-20 neurons in the right pedal ganglion. A total of only about ten immunoreactive neurons were located in other ganglia. Immunohistochemistry also demonstrated that APGWamide was present in the reproductive organs that participate in the storage or transport of sperm, including the small hermaphroditic duct (site of sperm storage before mating), the white hemiduct (also known as the copulatory duct), and penial complex. As a group, these data suggest that APGWamide may play a role in regulating male reproductive function in Aplysia, as it does in other gastropods.

L5‐67 and LUQ‐1 peptide precursors of Aplysia californica: Distribution and localization of immunoreactivity in the central nervous system and in peripheral tissues

Two genes (L5-67 and LUQ-1) that encode neuropeptide precursors have recently been shown to be expressed in a distinct and non-overlapping manner in the five left upper quadrant (LUQ) cells of the abdominal ganglion of Aplysia (Landry et al. [1992], J. Neurobiol. 23:89–101). By using wholemount immunohistochemistry and radioimmunoassay (RIA), the pattern of expression of these two genes was assessed at the protein level throughout the central nervous system (CNS) and in peripheral tissues of Aplysia californica. The distribution of LUQ-1 precursor-like immunoreactivity was fairly limited, occurring in the ventral LUQ cell (L5) and in a total of approximately 20 additional neurons in the abdominal and cerebral ganglia. L5-67 precursor-like immunoreactive material was more prevalent, appearing in a total of approximately 100 neurons distributed among each of the central ganglia. Identified L5-67-immunoreactive neurons included the four dorsal LUQ cells (L2-4 and L6) and two giant neurons (R2 and LPI1). In one group of cells, the H cluster of the cerebral ganglion, L5-67 immunofluorescence was substantially more intense in larger versus smaller animals, suggesting that this peptide precursor is subject to developmental regulation in certain neurons. Immunoelectron microscopic examination of the subcellular localization of L5-67 immunoreactivity in LUQ cell somata and axons revealed its association with dense-core vesicles (approximately 114 nm in diameter). In the periphery, L5-67-immunoreactive fibers were detected in specific regions of the circulatory system (auricle, ventricle, cristae aorta, anterior aorta) and the reproductive system (genital ganglion, large hermaphroditic duct, small hermaphroditic duct, ovotestis. The kidney and the intestine, two tissues in which considerable secretion and absorption occur, contained material immunoreactive to both L5–67 and LUQ-1 antisera. The localization of the two peptide precursors in these tissues differed substantially, with L5-67 occurring in widely ramifying varicose fibers, whereas LUQ-1 was found in restricted foci of fibers and in small spherical cells that appeared to lack processes. These results support previous findings concerning the heterogeneity of neurotransmitter phenotypes in the LUQ cells. Furthermore, they are indicative of a fairly broad role for the L5-67-derived neuropeptides, and a more limited role for the LUQ-1-derived neuropeptides, in the regulation of the visceral organ systems of Aplysia. © 1996 Wiley-Liss, Inc.

Effects of Temperature on Reproductive Neuroendocrine Function inAplysia californica

Egg laying in the gastropod molluskAplysia californicais a temperature-dependent behavior, facilitated by warm temperature and attenuated by cold. The purpose of this work was to determine which components of the reproductive axis controlling egg laying are affected by temperature. There were three neural/reproductive tissues investigated: (1) the head ganglia that transmit neural signals to the neuroendocrine bag cells, (2) the bag cells that synthesize and secrete egg-laying hormone (ELH), and (3) the ovotestis that extrudes eggs into the hermaphroditic duct in response to ELH. There was no significant effect of temperature on the ability of ELH to stimulate egg laying, suggesting that temperature does not alter responsiveness of the ovotestis to hormonal stimulation. There was evidence that the bag cells play a secondary role in mediating the effects of temperature on egg-laying behavior, that is, using both bioassays and radioimmunoassay for detection or measurement of ELH, hormone secretion was shown to be inhibited by cooler temperatures in some preparations. However, the inconsistency of this response suggested that the primary effect of temperature is upstream from the bag cells. Results from an experiment in which the head ganglia were chemically stimulated to activate bag cell electrical activity suggested that the primary site of temperature regulation lies within the head ganglia.

REPRODUCTIVE SYSTEM AND SPERMATOGENESIS IN THE OPISTHOBRANCH GASTROPOD RETUSA OBTUSA (MONTAGU)

The cephalaspidean opisthobranch Retusa obtusa has an ovotestis simultaneously producing eggs and spermatozoa. Reproductive organs are characterized by the hermaphrodite duct and seminal receptacle together joining the pallial glandular duct which is differentiated anteriorly to form the ‘albumen’ gland, membrane or capsule gland, and mucus gland. The duct of a copulatory bursa joins the common central chamber of this complex. Eggs presumably pass through extended tracts in the 3 glands to emerge at a hermaphrodite aperture in the right side of the mantle cavity. Spermatozoa also emerge at this aperture to a ciliated seminal groove along the right side of the head which, in turn, joins copulatory organs folded within the head and opening close behind the right cephalic tentacle: a muscular penial sac receives 4 elements of prostate gland. Spermatophores were never seen. Oocytes, surrounded by several thin follicle cells, reach 150–330 μ, m diameter in larger winter snails, mostly in the periphery of theovotestis. Spermatocytes and spermatids develop as clusters in association with accessory (Sertoli) cells. The acrosome appears in the centre of a dense anterior plaque, develops as a domed acrosome vesicle on a short peduncle and eventually becomes a terminal spike on the nucleus tip. The Golgi complex is seen sometimes near the early acrosome but more often behind the nucleus. Mitochondria aggregate first ahead of the nucleus but then form a mitochondrial derivative, with a glycogen helix, spiralled around the axoneme throughout the mid-piece of the tail. This region is marked off from the end-piece of the tail by the annulus. The nucleus becomes long, spiralled with a strong keel, and surrounds the centriolar derivative at the base of the axoneme.

The spermatogenic cycle and role of the hermaphrodite duct in sperm storage in two desert snails

Summary The desert snails Sphincterochila zonata and S. prophetarum are hermaphrodites which have a distinct spermatogenic cycle. Snails aestivate (240–280 days/year) throughout the dry season. In mid-summer (May) the gonad is small and completely inactive. In August and September whilst the snails are still dormant, the ovotestis increases in size and spermatogenesis commences, continuing until winter. Oogenesis occurs in winter (December/January) just prior to egg laying. Spermatozoa produced in August and September are stored in the seminal vesicle region of the hermaphrodite duct, thus enabling the snails to copulate and exchange spermatozoa immediately after the first winter rains. During aestivation the seminal vesicle region of the hermaphrodite duct and its constituent cells decrease in size and the duct becomes a region of sperm degradation. Electron microscopy has shown that the wall of the seminal vesicle is composed of two types of cell which undergo considerable morphological change during the different phases of the reproductive cycle.

Morphological investigations into Floriceps minacanthus (Trypanorhyncha: Lacistorhynchidae) with analysis of the systematic utility of scolex microtriches

Specimens of Floriceps minacanthus Campbell & Beveridge, 1987 are reported from Carcharhinus melanopterus (Quoy & Gaimard, 1824) taken in the waters surrounding the island of Kirimati in the Republic of Kiribati in the Central Pacific Ocean. This represents a new host and a new locality record. The description of this species is expanded to include the presence of an ovary which is bilobed in cross section and a hermaphroditic duct. The surface features were examined by scanning electron microscopy. With the exception of the lateral margins of the bothridia and the apical region of the scolex, the scolex was found to be covered with palmate microtriches interspersed with filiform microtriches. The palmate microtriches varied in number of digitiform extensions depending on location. Elongate, bifid microtriches were present in the transition zone between the proximal and distal surfaces along the lateral margins of the bothridia. The apical region of the scolex was covered with filiform microtriches. The surface of the anterior margin of the strobila was covered with broad, flattened scale-like structures. The pattern of microthrix distribution was repeated for each of the bothridia of an individual, and this pattern was intraspecifically invariable. Comparison of our results with those from the seven other trypanorhynch species examined by previous authors with SEM indicates that there is much interspecific variability in both the morphology of microtriches present as well as their location on the scolex. This, coupled with the lack of intraspecific variability, confirms that these structures are systematically informative.

Synaptic actions of identified peptidergic neuron R15 in Aplysia. III. Activation of the large hermaphroditic duct

The purpose of the study described in this and the preceding two companion papers was to determine the synaptic actions of neuron R15, an endogenously bursting neurosecretory cell in Aplysia, as a step toward determining its physiological function. The results described in this paper demonstrate that activity in R15 activates anterograde peristaltic movements in the segment of the large hermaphroditic duct through which eggs move during egg-laying behavior. This action is mimicked by R15 alpha 1 peptide, a putative transmitter of R15. The neuroendocrine bag cells, which initiate egg laying when they fire in a population burst, have been shown by others to excite R15. Our data suggest that R15 mediates excitatory effects of the bag cells on the large hermaphroditic duct. Taken with the results of the two companion papers, these data support the hypothesis that R15 integrates various aspects of egg-laying behavior. The desensitization of R15's postsynaptic actions may complement the long-lasting refractoriness of the bag cells described by others, with both effects contributing to the episodic nature of egg laying.

Distribution and characterization of pedal peptide immunoreactivity in Aplysia

Pedal peptide (Pep) is a very abundant neuropeptide in Aplysia. A radioimmunoassay (RIA) was developed to quantify Pep-like immunoreactivity (IR-Pep) in tissue extracts. IR-Pep was present in very high concentrations in the central nervous system (CNS) and two peripheral tissues: the large hermaphroditic duct (LHD) and the foot. RIA of fractions from high-pressure liquid chromatography (HPLC) indicated that Pep itself was the predominant immunoreactive species in each of these tissues. Lower concentrations of Pep were found in a number of other peripheral tissues. Incorporation of labelled amino acid indicated that Pep was synthesized in the LHD, whereas Pep in the foot was synthesized primarily in central neurons and transported to the foot. IR-Pep was further localized by immunocytology. All peripheral IR-Pep appeared to be associated with neuronal fibers, most commonly varicose axons. Immunoreactive innervation of the LHD and foot was particularly dense but positive staining was also observed in other tissues including tegument, gill, gut, and heart, IR-Pep innervation in all tissues including the LHD appeared to be localized predominantly in muscular portions of the tissue. Spontaneous contractions of isolated LHD were accelerated by the application of Pep. Pep appears to act as a transmitter or neuromodulator at a number of different sites in Aplysia.

Fine structure and possible functions of the hermaphrodite duct of some pulmonate snails (Mollusca: Gastropoda)

The hermaphrodite duct of pulmonate snails connects the ovotestis to the fertilization pouch. The duct is typically divided into three zones; aproximal duct which leaves the ovotestis, the middle duct (seminal vesicle) and the distal ovotestis duct. The seminal vesicle forms the major portion of the duct and is thought to store sperm prior to copulation. In addition the duct may also play a role in sperm maturation and degredation. Although the structure of the seminal vesicle has been described for a number of snails at the light microscope level there appear to be only two descriptions of the ultrastructure of this tissue. Clearly if the role of the hermaphrodite duct in the reproductive biology of pulmonatesis to be understood, knowledge of its fine structure is required.Hermaphrodite ducts, both containing and lacking sperm, of species of the terrestrial pulmonate genera Sphincterochila, Levantina, and Helix and the marine pulmonate genus Siphonaria were prepared for transmission electron microscopy by standard techniques.

Chimaerarhynchus n. g. andPatellobothrium n. g., two new genera of trypanorhynch cestodes with unique poeciloacanthous armatures, and a reorganisation of the poeciloacanthous trypanorhynch families

Chimaerarhynchus rougetae n. g., n. sp. is described fromSqualus acanthias andCentrophorus sp. from the coast of Senegal, and differs from all other trypanorhynch genera in having a chainette composed of dissimilar elements, that is, double-winged hooks alternating with pairs of hooks each with a single lateral wing. The new genus is allocated to the Gymnorhynchidae Dollfus, 1935.Patellobothrium quinquecatenatum n.g., n. sp. is described from the spiral intestine ofSphyrna mokarran from Darwin, Northern Territory, Australia and plerocerci fromRachycentron canadus from Queensland, Australia. The genus is distinguished from all others in possessing five chainettes. It is allocated to the family Mustelicolidae Dollfus, 1969. The relationships of all genera of trypanorhynchs possessing chainettes are discussed, and they are divided into three groups: (1) Dasyrhynchidae Dollfus, 1935, Lacistorhynchidae Guiart, 1927, Mustelicolidae and Hornelliellidae Yamaguti, 1954 are considered closely related since all genera possess two bothridia, a hermaphroditic duct and have hollow hooks; (2) Gymnorhynchidae, amended to contain onlyGymnorhynchus Rudolphi, 1819 andChimaerarhynchus n.g., is distinct in possessing four bothridia, an accessory seminal vesicle and hollow hooks; (3) Mixodigmatidae Dailey & Vogelbein, 1982, amended to includeMixodigma Dailey & Vogelbein, 1982 andHalysiorhynchus Pintner, 1913 has four bothridia, lacks seminal vesicles and a hermaphroditic duct and has solid hooks.

Two new digenetic trematodes from Australian freshwater fishes with notes on previously described species

Austrohalipegus anguillicola gen. et sp. nov. is described from the stomach of Anguilla reinhardtii Steindachner. Austrohalipegus is distinguished from other derogenid genera by the absence of filaments on its eggs, by the presence of blindly ending caeca, by having the ventral sucker in the middle of the body, by having the sinus-sac enclose only the hermaphroditic duct, and by the uterus which does not extend posterior to the vitellarium. Austrohalipegus anguillicola is distinctive in having a large temporary sinus-organ formed by a completely eversible hermaphroditic duct. Isoparorchis hypselobagri (Billet) is recorded as juveniles of 1–3 mm in length from the coelom and as larger juveniles and adults from the swim bladder of Tandanus tandanus Mitchell. The miracidium is typically hemiuroid and has a crown of apical spines and cilia in lateral bunches. Experimental infections in which the prosobranch snails Posticobia brazieri and Melanoides tuberculatus were fed embryonated eggs produced infections of mother sporocysts. It is postulated that the life-cycle includes an obligate period of development in the coelom of the definitive host for the Australian form of the species. Stegodexamene watsoni sp. nov. is described from the intestine of Maccullochella peeli (Mitchell). It is distinguished from the two other species of this genus by its considerably larger cirrus pouch and its more extensive vitellaria. Burnellus trichofurcatus (Johnston and Angel) is recorded from new hosts, Arius graeffei Kner and Steindachner and Neosilurus ater (Perugia). Aspects of its biology are discussed. Pretestis australianus Angel and Manter is recorded from a new host, Scortum hilli Castelnau, extending the known range of this species.

Functional protandry and seasonal reproductive cycle in Solatopupa similis (Bruguière) (Pulmonata Chondrinidae)

Abstract The study of the gamete maturation and the seasonal reproductive cycle of Solatopupa has been carried out by the histological analysis of both the ovotestes and the genital ducts of specimens which were periodically sampled from a natural, outcrossing population. S. similis has been demonstrated to be a true hermaphrodite, since both types of its gametes begin to differentiate together and probably undergo simultaneously the meiotic prophase; however, it could be considered functionally protandrous because male gametes come to maturity in spring and summer, while egg maturation and growth is delayed until the late winter. Mature sperms are stored throughout the year in a portion of the ovotestis duct (or first hermaphrodite duct) which functions as a seminal vesicle: thus, functional protandry is certainly not important as a self‐sterility mechanism. The behavioural and adaptive significance of this pattern of gametic maturation and auto‐sperm storage are also discussed.

Immunoreactivity of the hermaphroditic gonad of the snail Helix aspersa M�ller towards antibodies raised to fragments of pre-pro-opio-melanocortin

Male and female germinal cells of the active hermaphroditic gonad of a snail (Helix aspersa Muller) reveal a positive immunoreactivity to some antibodies raised against biologically active peptides related to pre-pro-opiomelanocortin of vertebrates. All but the oldest cells of the different spermatogenetic and oogenetic stages are methionine-enkephalin-immunopositive, whereas only the young oocytes are α-MSH- and 17–39 ACTH-positive. Sometimes some male cells show an 1–24 ACTH positivity. Structures other than germinal cells also react with some antibodies: for example, the nurse cells are β-MSH-immunoreactive, the nerve fibers surrounding each acinus and the hermaphrodite duct are both 17–39 ACTH and FMRF amide positive.

Egg-laying hormone genes of Aplysia: evolution of the ELH gene family

Evolution of the egg-laying hormone (ELH) gene family was examined in the genus Aplysia using genomic Southern blotting, gene cloning, and immunocytochemical techniques to identify and characterize homologous sequences. Most of the species examined have fewer than the 4-5 ELH-related genes present in the A. californica genome (Mahon et al., 1985; Scheller et al., 1983). In A. parvula there are 2 ELH genes, and unlike A. californica, no sequences were found to encode the A or B peptides. The 2 A. parvula ELH genes share at least 90% DNA sequence homology, while the homology between the A. parvula and A. californica ELH genes is 71%. The structural organization of the A. parvula ELH precursor is quite similar to the ELH precursor of A. californica, with all but one of the potential proteolytic cleavage sites conserved. The overall amino acid homology between the A. parvula and A. californica ELH precursors is 66%; however, the alpha and beta bag cell peptides, as well as ELH, are more highly conserved, suggesting that these peptides have important physiological and behavioral roles within both Aplysia species. Immunocytochemical studies indicate that the A. parvula ELH genes are expressed in 2 bag-cell-like clusters of about 40 neurons each in the abdominal ganglion. There does not appear to be an atrial gland in A. parvula; however, ELH-immunoreactive peripheral neurons and their processes are observed along the perimeter of the large hermaphroditic duct.