Published accounts of the reproductive systems of various species of New Zealand Athoracophoridae generally agree fairly closely. Most accounts show the prostate and oviducal glands as discrete structures, with only minor differences in morphology between the species. An exception is Pseudaneitea ramsayi (Climo, 1973) in which the prostate gland and the oviducal gland (called the uterus in Climo's description) form an elongate, intertwined, irregular complex up the central axis of the reproductive system. A similar pattern can be seen in the reproductive system of Athoracophorus bitentaculatus and this arrangement is quite different from that seen in Pseudaneitea papillata, for example (Burton, 1962). It is still not clear whether a basic difference in the form of the reproductive system does exist, or whether it is due to seasonal or growth factors.

Functional aspects.

Athoracophorus bitentaculatus, like other pulmonate Gastropods, is hermaphroditic, and has a complex reproductive system. This system appears to be capable of producing both eggs and sperm for a considerable period of the year, at least from Autumn through Winter to Spring. It is highly likely that a slug will mate a number of times through the breeding season. When this mating occurs, a number of events take place within the reproductive system to facilitate it.

In the male system, sperm produced by the gonad are stored in the hermaphrodite duct, which becomes distended with sperm, except for the portion nearest the albumen gland. The passage of sperm through the fertilisation sac, down the male duct, and into the vas deferens and penis is obviously not a continuous process, as no sperm were found in any of these organs. Such a movement of sperm through the reproductive tract probably occurs only just prior to copulation, or during copulation itself. While slugs have been observed in copulo, no courtship behaviour patterns have ever been recorded in the Athoracophoridae. However, elaborate courtship sequences have been described for many slugs, and it seems that one function of courtship is synchronisation of the physiology of the mating partners (Runham and Hunter, 1970). It seems highly likely that such a courtship sequence occurs in the Athoracophoridae as well.

The movement of sperm through the reproductive tract is probably passive, as all ducts are either ciliated (hermaphrodite duct, male duct, vas deferens) or muscular (penis). This movement of sperm is aided by secretions from various sources, notably the prostate gland and the vas deferens. The prostate gland secretes the seminal fluid, the function of which is uncertain. It is generally believed to be nutritive (Kugler, 1965), although it contains a number of non-nutritive constituents whose function is unclear (J. M. Cummins, pers. comm.). In Philomycus carolinianus, subepithelial glands of the spermatic groove produce mucus which binds the sperm together into a sperm thread. Similar subepithelial mucus glands are present in Athoracophorus bitentaculatus.

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In summary, the sperm is produced by the gonad, stored in the hermaphrodite duct, probably until the onset of courtship, passed by ciliary action through the fertilisation sac and along the spermatic groove to be bound by mucus secretions into a sperm thread, then reaches the vas deferens at the bifurcatio spermoviducti, and passes down into the eversible penis for insertion into the vagina of the mating partner. Once inserted into the vagina, the sperm mass enters the spermatheca, and is apparently stored there until required. The exact mode of sperm transfer into and up the duct of the spermatheca is not known, but the penis would certainly extend as far as the opening of the duct when fully inserted into the vagina, and it is conceivable that the penis could inject the sperm mass directly into the spermatheca. Holm (1946) in studies on Lymnaea stagnalis appressa Say, observed that in comparatively young snails, nearly all the sperm transferred at the time of copulation passed into the receptacle, and few sperm were seen in the upper vagina. Furthermore, the sperm in the spermatheca of Athoracophorus bitentaculatus is, for the most part, still in a compact, mucus-bound mass, and it seems unlikely that they could swim unaided into the receptacle.

Ikeda (1937) determined that in the slug Meghimatium bilineatus the spermatophores received during copulation were retained for a period in the genital atrium, where the sperms were loosened from the sperm mass, and lost their tails. The tailless sperms were then passively conveyed to the spermatheca and stored until oviposition. No tailless sperm were observed in Athoracophorus bitentaculatus and this agrees with the finding of Kugler (1965) for the slug Philomycus carolinianus. In A. bitentaculatus, the sperm mass retained within the spermatheca tends to break up under the influence of the secretions of the spermathecal wall. It is clear that sperm may be moved passively up to the point at which they enter the spermatheca, through either ciliary action or muscular movement. However, the lumen of the uterus is thickly coated with mucus, and its walls are non-ciliated. Presumably, the sperm swim unaided up the uterus to the fertilisation pocket, and if this is the case it follows that the function of the secretions of the spermathecal wall may be twofold, in that they loosen the sperm from the sperm mass and induce sperm capacitation.

The female system is functionally less complex. In pulmonates in general, there is a continuous production of ova, sperm and nutritive cells in the mature gonad, except towards the end of the breeding season (Runham and Hunter, 1970). Smith (1966) observed that in Arion ater maturing gonads commence sperm production before ova appear, and this is also the pattern in Athoracophorus bitentaculatus. However, A. bitentaculatus does not show the clear separation of the male and female phases of reproduction seen in Arion ater, and thus conforms more closely to the generally accepted pulmonate pattern.

The egg is considerably larger than the efferent ductule. However, the efferent ductule is heavily ciliated and, like the hermaphrodite duct, is apparently capable of some distention. As the egg is oval, passage of the egg through the narrow efferent ductule probably presents little difficulty. The hermaphrodite duct is normally packed with sperm, but as copulation takes place some time before egg laying, sperm would be cleared from the hermaphrodite duct in time to allow the passage of the ova for fertilisation in the fertilisation pocket. The fertilised ova then page 16receive the nutritive secretion from the albumen gland, and pass to the oviducal gland to receive a layered, gelatinous shell. The eggs then pass down the uterus to be laid in clusters of 15 to 20; they are round, papillate, gelatinous, light yellow, and up to 3 mm. in diameter.

Overall the organisation of the reprodutive system of Athoracophorus bitentaculatus shows a striking similarity to that of other slugs, such as Agriolimax reticulatus and Arion ater. Some differences do occur, such as the enclosure of the penis in a penis sheath and the partial separation of the male and female ducts, but the organisation and histology of the reproductive tract of these species is similar enough to underline once again the conservativeness characteristic of the Mollusca.