MUSEUM OF COMPARATIVE ZOOLOGY. 487 



the expulsion of the nucleoli." * "We distinguish therefore equally in 

 both cases the formation of a generation in which the two sexes are separate 

 cells, and then the union of two sexual unicellular individuals, of different 

 origin, to form an asexual cell, which then goes on dividing asexually for 

 many generations until the original energy is exhausted." The q%^ 

 really becomes female only upon the discharge of the male direction 

 cells. It is important to know whether in the development of the 

 spermatozoa the 'mother cell breaks up into two portions, one of which 

 becomes the male part, while the other remains separated. " The few 

 available observations fulfil our expectations, for they describe a ' Mut- 

 terkern ' (female element) which remains behind and is aborted." 



In a provisional theory of generation McCrady ('77) concludes that 

 the act of generation consists in the actual conjugation of at least two 

 protozooids (one ovum, and one, or in most cases several spermatozoa). 

 The result is twofold: (1.) the combination of the nucleus of the sperma- 

 tozoon with the germinative vesicle of the ovum (this resultant is the 

 future animal) ; and (2.) the aggregation of the yolk protoplasm with the 

 protoplasm of the spermatozoa, these together constituting a store of 

 foo for the immediate nourishment of the newly arisen animal,, which it 

 proceeds to appropriate in the manner of a rhizopod. This appropria- 

 tion of the whole provision is the process called segmentation. It is 

 probable that in the conjugation the germinative vesicle and the sper- 

 matozoon (or its nucleus) disappear and cease to exist as such. In their 

 stead arises the new animal, or protemhryo. This new animal may pre- 

 sent itself under one or the other of three conditions : {a) as a clear 

 mass of protoplasm within the yolk mass, — the embryonal vesicle of 

 Wagner ; (6) as a nearly uniform layer of protoplasm, completely enclos- 

 ing the yolk mass ; or (c) as a combination of a and h, in which the 

 central and peripheral portions of protoplasm are connected with radial 

 threads of the same. These are respectively styled Ento-, Ecto-, and 

 Fanto-jprotemhryo. 



With the fundamental correction now possible, that it is not the ger- 

 minative vesicle, but the female pronucleus, which unites with the sperm 

 nucleus, this view appears to approach that which Strasburger has more 

 recently promulgated ; but how far it comes short of a just appreciation 

 of the mutual relations of nutritive substance, living protoplasm, and 

 nuclear substance, is too apparent to demand discussion. There does 

 not seem to have been here, any more than in the paper last reviewed, 



* The nature of the argument to be drawn from the " Kernspindel" has been 

 stated by Whitman ('78% p. 46). 



