16 HARLEY N. GOULD 



cells (figs. 2, 3, etc., /). The nuclei are sometimes hard to dis- 

 tinguish from the smallest of the primordial male germ nuclei, 

 but can usually be identified by their deeper stain. After pro- 

 longed staining in iron haemotoxylin they will remain a dense 

 black when the germ nuclei have bee a so destained that their 

 chromatic pattern is clear; and in Delafield's haemotoxylin the 

 follicle nuclei take a deeper blue than the germ nuclei. No mi- 

 totic figures have ever been found which could be ascribed to the 

 follicle cells, although there are certain periods in the sexual 

 cycle (e.g. at the beginning of the female phase) when their 

 number is rapidly increased. 



In this connection we must consider the relation of the germ 

 ceils to the so-called 'basal cells' described in certain Molluscs. 

 The authors of the earliest work on the origin of germ cells in 

 Molluscs were of the opinion that the spermatogonia of the male 

 arose from the large 'basal nuclei' found in the germinal layer. 

 Some even derived the spermatogonia from these elements by 

 amitosis (Von Brunn, '84). Other writers on the contrary 

 described the basal nuclei as arising from spermatogonia. Lee 

 ('97), Ancel ('03), de Bruyne ('03) and Kleinert ('09) interpret 

 their material as showing that the germ cells and basal cells 

 have a common origin out of an indifferent germinal epithelium. 

 Kuschakewitsch ('13) states that he has followed the formation 

 of the basal cells in Vermetus out of an indifferent layer; and is 

 of the opinion that the young, relatively small basal cells have 

 the power of mitotic division ; but when they have reached their 

 full development, though they may make an effort at such a 

 division, it is never completed. Earlier authors have also ex- 

 pressed the opinion that the basal cells have lost the power of 

 mitotic division. These basal cells are generally considered to 

 be nutritive elements. Reinke ('14) traces the apyrene sperma- 

 toblasts of Strombus back to them. 



In Crepidula the writer does not find an ''indifferent germinal 

 epithelium" of the nature described by other authors; but rather, 

 two different categories of germ cells lying in what appears to be 

 a follicular syncytium whose nuclei are small and stain charac- 

 teristically. There are no large basal nuclei except the nuclei 



