REPRODUCTIVE SYSTEM AND SEXUAL SUCCESSION OF L. BULIMOIDES 185 



clearing in xylol. The condition of the gonad could be ascertained by rapid inspection of the cleared 

 animal, and each specimen assigned to its stage in Table 7. The results were checked by correlating 

 the appearance of the stained gonad with the condition of the genital tract and gonad in a large series 

 of sectioned specimens. 



Table 7. Stages in the sexual succession of Limacina bulimoides 



1. No sexual development at all. Gonad represented only by a small cap of undivided pregerminative cells. 



2. Less than one gonadial whorl. An apical mass of lighter staining primary spermatogonia, which in 

 lower part of gonad have begun to divide into darker-staining secondary spermatogonia. 



3. Less than two gonadial whorls. Primary spermatocytes arranged in spherical clusters lying freely in the 

 lumen of the gonad. Penis and prostate absent or very tiny. 



4. More than two gonadial whorls. Gonad contains primary spermatocytes and spermatids. Stained 

 appearance never shows lighter areas of bundles of sperm tails. Penis and prostate fairly large. Female 

 ducts present, but usually non-glandular. 



5. Mature male. Most of gonadial lumen occupied by platelets of mature sperms. Penis and prostate 

 large. Oocytes which have now appeared, are increasing in size (c. 70-100 /x) but still parietal and with 

 no dark granular yolk inclusions. Epithelium of female duct filled with undischarged secretion. 

 Receptaculum seminis usually not visible. 



6. Pure Female. Gonad containing entirely (or almost entirely) oocytes, with at times a few clusters of 

 sperms left behind. Spermatogenesis entirely ceased. Many ova discharged into lumen of gonad, and 

 of large size (c. 130/i) with dark-staining yolk inclusions. Penis and prostate lost. Mucous gland large 

 and distended with secretion. Receptaculum seminis large and tightly filled. 



Table 8. Percentage distribution of sexual stages among size groups in Limacina bulimoides 



The data of Table 8 have been expressed diagrammatically in Fig. 10 in a form easily comparable 

 with Hsiao's diagram for L. retroversa (Hsiao, 1939&, p. 286). In Fig. 11 is further shown the 

 distribution of the four sexual types, here designated females, mature males, developing males and 

 sexually undifferentiated individuals, among the three largest samples from the March cruise. The 

 form of the diagram should enable easy comparison with data obtained in the second survey, and with 

 subsequent data obtained for this or other species of Limacina over the twelve months of the year. 



(ii) The Genital Ducts (Fig. 12) 



The animals used for description are chiefly those of stage 5 shortly before female maturity. The 

 glandular genital duct already bulges into the pallial cavity, where later, at stage 6, it becomes pressed 

 closely against the pallial mucous gland (PALL.G.) on the roof of the mantle, and filled with masses 

 of colourless secretion. As it appears in Fig. 12, looking down upon it lying on the pallial cavity floor, 

 the mucous gland, which is the most obvious part of the genital tract, consists of two limbs. The 

 largest is the descending tubular limb (MUC.D.), very thick-walled, tapering forward to the common 

 genital aperture (C.GEN.). It acts as an hermaphrodite genital duct, as in primitive hermaphrodite 

 gastropods, and sperms traverse it before the passage of eggs. It is translucent white in colour. The 



