REPRODUCTIVE SYSTEM AND SEXUAL SUCCESSION OF L. BULIMOIDES 193 



par un double conduit — d'une parte avec la gaine du penis par un conduit relativement court et d'autre 

 part avec le penis par un tube excreteur formant une anse assez considerable.' In Haminea, Doridium 

 and Gastropteron there is also a prostate of the appendage type, and a similar structure was described 

 briefly by Tesch (1950) and further investigated by the writer (unpubl. obs.) in the gymnosomatous 

 pteropod Clione limacina. It is apparently lacking in Aplysia, the pleurobranchomorphs and in the 

 bullomorph Acera, and also in the primitive Actaeon, which in many features of its genitalia would 

 seem to stand apart from other tectibranchs. The condition in the Thecosomata, with the prostate so 

 closely involved in the actual penial sac, would appear to be unique. Its relations are likely to be much 

 better understood after the examination of more species of pteropods, and especially after Lloyd's 

 work has been published, which will give a full and detailed review of the genitalia in a wide range of 

 opisthobranchs. 



The histology of the prostate in Limacina (Fig. 13^) is relatively simple; there is one type of gland 

 cell and at no stage could ciliated cells or cilia be identified at all. The glandular cells are columnar, at 

 stage 5, 75 ju, in length. The nuclei are large rounded and deeply staining, forming a single basal row. 

 The inclusions in the cytoplasm vary in size extremely; the largest are about 10 /x across and the smal- 

 lest extremely fine, much less than 1 /x. Their size in a given cell is relatively constant, and sometimes 

 in a transverse section there appears a sector of cells containing smaller granules, very distinct from 

 the rest. The free surface of the cells is fiat or bulges slightly into the lumen — it is broken only by the 

 passage of contents from the mature cell. The staining reaction is little if any with haematoxylin, pink 

 in eosin, and orange after eosin-Orange G. The epithelium of the prostate lies on a very thin con- 

 nective tissue sheath, sparsely muscular. Outside the prostatic tube, facing towards the lumen of the 

 penial sac, there is another layer of glandular epithelium (PR. EXT.). The base of this layer lies 

 against the base of the prostatic epithelium, forming a sleeve wrapped around about half the circum- 

 ference of the prostate along the best part of its length. The secretion from these cells is similar to that 

 produced by the prostate, and it is discharged directly into the lumen of the penial sac. The height 

 of this layer reaches 10/x, and the cell nuclei are rather flattened, only about half the size of the 

 prostate nuclei. Towards the edge of the epithelial zone the height of the cells diminishes and they 

 merge gradually with the very thin glandular epithelium, which seems to line the whole of the rest of 

 the penial sac, being reflected both over the coils of the prostate and the ridges and furrows of the sac, 

 and running through the intromittent portion of the penis itself. Here the cell height is less than 5 /x, 

 and the cell boundaries are very indistinct. The cytoplasm is packed with tiny granules of secretion, 

 some of them highly refractile, and staining like those of the prostate. The nuclei form a flattened basal 

 row, and the free border of the cells, when fixed in formalin, tends to break away with the shedding 

 of its contents. Whether it is ever ciliated is not easy to determine, but even in the best fixed material 

 no cilia were detected anywhere in the prostate or penial sac. So far as is known, Limacina has never 

 been observed in copulation, and our knowledge of pairing in a pteropod is restricted to the one species 

 Clione limacina. It would be of great interest to examine the relations of the male organs in the 

 everted condition and to find how the supposed intromittent organ is brought into use. We may, how- 

 ever, reasonably suggest from examination of the structure of the penial sac the course taken by the 

 sperms, which are presumably liberated freely into the general cavity of the sac when brought to it 

 by the seminal groove. Together with prostatic secretion they enter the intromittent organ at its base. 

 The secretion of the prostate, and that of the general lining of the sac evidently contribute the 

 nutritive portion of the semen, and the sperm finds its way through the lumen of the sac by several 

 rather tortuous paths between the coils of the prostate, to the base of the penis. The arrows in Fig. 1 5 

 suggest the general course taken by the sperm after it is received into the sac and before ejaculation. 



