REPRODUCTIVE SYSTEM AND SEXUAL SUCCESSION OF L. BULIMOIDES 191 



figures of a dissection of the penis in Limacina helicoides are also wanting in detail. A prostate is 

 nowhere mentioned by these authors, though Hsiao correctly points out its presence in retroversa. 



Fig. 15 must serve to illustrate schematically the interior of the penis in L. bulimoides. It represents 

 a stereogram of the whole sac opened longitudinally and slightly obliquely. The ciliated seminal 

 groove enters at the male aperture (M.AP.) and through the same aperture the intromittent portion 

 of the penis is extruded. The chamber of the sac into which the sperm flows from the seminal 

 groove is to a large extent occupied by the thick tubular prostate, which is usually coiled in an S or 

 doubled upon itself in the retracted and fixed condition. It is slung to the wall of the sac by a long, 

 winding septum and the lumen of the penial sac consists of a series of narrow slits and spaces un- 

 occupied by the prostate. The lumen of the prostate itself is a narrow slit, rounded or crescentic in 

 cross-section. It receives the secretion from the lining cells and communicates apparently only at its 

 proximal end with the sperm canal. So far as can be made out from reconstruction, the distal end of 

 the prostate appears to end roundly and bluntly. At the bottom of the penial sac there is a flask-like 

 expansion, with which the inner end of the prostate communicates, and towards which converge also 

 the interstices of the sac surrounding the prostate. This flask-like expansion (LU.PEN.) is prolonged 

 into a conical or pointed tube, perforate throughout and surrounded by a layer of vacuolated tissue, 

 clear-staining and cartilage-like. While no doubt flexible, this structure appears to be the most rigid 

 part of the male apparatus. It terminates at one side of the prostate, opening directly into the lumen 

 of the penial sac, some distance inside the male aperture. Though in the absence of observations of 

 copulation, it is difficult to reach a final conclusion, it would appear, from a comparison with similar 

 ' cartilage '-supported structures in Clione, that this is the intromittent portion of the male apparatus. 

 It is the only part that is not tied down by the insertion of the prostate and that is likely to be eversible 

 from the male opening. Into it, as has been said, converge the folds leading the sperm inwards and 

 between the coils of the prostate ; and at its base opens the duct of the prostate itself. 



The histological structure of this part of the penis is illustrated diagrammatically in Fig. 15. The 

 main thickness of its wall is formed by a row of large wedge-shaped or columnar vacuolated elements. 

 These are actually the ' cells ' of molluscan cartilage, a modification of connective tissue, resembling 

 a stiff parenchyma, developed — as in the buccal mass — in most regions where stiffness combined with 

 flexibility is required. The lumen of this part of the penis is lined with a low epithelium of cubical cells 

 of the same glandular type (see below) as cover the rest of the interior of the penial sac. At the base 

 of the sac, and spreading along its wall from the intromittent portion of the penis runs an extension of 

 the cartilage-like connective tissue. 



It seems to be one of the characteristic features of the genital system of primitive tectibranchs that 

 the ' prostate ' develops as a long appendage to the penis quite separate from the rest of the glandular 

 genital duct. Such a condition is in strong contrast to that of the primitive Pulmonata, where the 

 prostate— as in the prosobranchs— retains a close relation with the anterior part of the pallial genital 

 tract. Here at first it forms part of a common mucous-prostatic duct, possessing a single lumen con- 

 veying both eggs and sperm ; later — in the higher pulmonates it becomes cut off as a separate male 

 channel. In both pulmonates and opisthobranchs the nature of the prostatic glandular cells appears 

 to be essentially similar. Their function is probably identical, and there would seem to be no good 

 reason to restrict the descriptive term 'prostate ', following the suggestion of Hubendick (1948), to the 

 prosobranch or pulmonate type, and to exclude from this category the male accessory gland of 

 tectibranchs. In Philine, according to the description by Guiart (1901), there is a tubular prostatic 

 gland opening as an appendage from the base of the penis, with which it makes a double connection. 

 'Chez la Philine aperta la prostate se compose d'un long tube glandulaire qui forme de nombreux 

 replis dans la cavite cephalique de l'animal, mais le canal central de cette prostate se trouve en rapport 



