i 9 8 DISCOVERY REPORTS 



paucidens and Limacina bulimoides offshore. The latter was by far the most abundant species and 

 greatly outnumbered the related L. inflata. Its ecology and distribution are discussed. There is 

 evidence that the diurnal depth migrations performed by the Limacinidae are very much shorter than 

 in the Cavoliniidae already investigated, and there appears at night to be a size-depth division of the 

 population, the larger individuals making a journey to the surface, and the smaller individuals 

 remaining predominantly lower down as in their day-time distribution. The gymnosomatous pteropod 

 Pneumodermopsis paucidens is a species that has not been found commonly in past collections, and a 

 taxonomic description and fresh figures are given. 



In the second part of this paper the reproductive system and sexual succession of Limacina buli- 

 moides are described in detail. The genital ducts are typical of the lower level of evolution in both the 

 opisthobranchs and the pulmonates, and consist of a little hermaphrodite duct and a glandular herma- 

 phrodite tract comprising albumen gland, fertilization pouch and mucous gland. A receptaculum 

 seminis forms a large diverticulum in the mature female. The penis is a complicated structure, and 

 with it is associated a tubular prostate gland. These structures are for the first time described fully, 

 with details of their histology. Limacina is a protandrous hermaphrodite and six sexual stages are 

 recognized, all of which are present in the March population, ranging from sexually undifferentiated 

 individuals of small size, through various stages of male development, to the pure females which are 

 the largest individuals. A comparison is made between L. bulimoides and L. retroversa as reported 

 upon by Hsiao, and a short discussion is added, dealing with the sexual succession in Limacina and the 

 problem of the evolution of sex in the Gastropoda as a whole. 



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