l6o O. C. GLASER. 



Pahtdina. These differences in development first become man- 

 ifest by the occurrence of two sizes of primary spermatocytes, the 

 larger of which give rise to the oligopyrene spermatozoa, whereas 

 the smaller ones give rise to the eupyrene forms. When the 

 larger primary spermatocytes undergo maturation no reduction 

 takes place, but the normal number of chromosomes (fourteen 

 for Paludina) appears at the nuclear plate. These chromosomes 

 are so distributed in the ensuing division that one of the resulting 

 daughter cells (secondary spermatocytes) has four and the other 

 has ten. When the secondary spermatocytes divide to form the 

 spermatids, only one of the chromosomes of the secondary sper- 

 matocytes undergoes division, all the others (three for one class 

 of spermatocytes and nine for the other class) degenerate. In 

 this way it happens that the nucleus of the oligopyrene sperma- 

 tozoa is composed of a single chromosome, whereas that of the 

 functional eupyrene sperms has seven. 



Fasciolaria, in company with a large number of other proso- 

 branchs, has two kinds of spermatozoa, and - there can be little 

 doubt that these correspond respectively to the oligopyrene and 

 the eupyrene sperms of Paludina. What the reason for this 

 dimorphism may be is not clear, but so far as I can see, there is 

 no evidence to show why it might not also occur among eggs, 

 particularly of a form presenting such well marked differentiation 

 of its male sexual elements as Fasciolaria does. 



That Fasciolaria has two kinds of primary oocytes which differ 

 most remarkably in their reactions with spermatozoa, and con- 

 sequently in their ultimate fate, is beyond dispute. This difference 

 may possibly be due to an homology between the infertile oocytes 

 and those primary spermatocytes which give rise in the manner 

 described by Meves to the oligopyrene spermatozoa. Whether 

 further investigations establish this homology or not, the presence 

 of the infertile eggs is the keystone of the conditions that deter- 

 mine cannibalism. The origin of this process therefore is to be 

 sought in those circumstances that determine the formation of 

 the sterile ova. That these ova should be ingested follows from 

 the automatism of the larvae, based on structures much older than 

 the habit of cannibalism, and not to be explained by it. The 

 persistence of those processes which give rise to the nutritive ova 



