173 THE EVOLUTION OF AIAN. 



lization. One party affirms that it is expelled from the 

 egg-cell, the other that it dissolves in the yelk. Some are 

 of opinion that it disappears entirely, others, that it only 

 does so partially. 



We cannot here enter into the various views which have 

 recently been formed as to this remarkable incident in fertili- 

 zation, the examination of which presents great difficulties. 

 Those who are particularly interested in it may be referred 

 to valuable works on this subject by Auerbach, Butschli, 

 Hertwig, Strasburger, and others. ^° Here we can only 

 briefly indicate the view which at present appears most 

 probable. Most students of this point now assume as a 

 universal incident in fertilization that the germ-vesicle, the 

 original kernel of the egg-cell, disappears before fertilization, 

 being either expelled from the egg or dissolved in the yelk. 

 Either no part of the egg-cell, or only the germ-spot 

 (^nucleolus), remains as a defined part in the yelk. Accord- 

 ing to Hertwig and others, this germ-spot amalgamates with 

 the sperm-kernel, or the kernel of the intruding sperm -cell, 

 and this amalgamation gives rise to the kernel of the 

 parent-cell. On the contrary, according to other observers, 

 the parent-kernel (cytococcus) is an entirely new formation 

 in the protoplasm of the parent-cell (cytula, Fig. 21). 



At present, therefore, the majority of observers assu^ne 

 that between the oriorinal nucleated eo^i^-cell and the 

 known nucleated parent-cell there is a stage in which there 

 is no real cell-kernel or nucleus, and in which, therefore, the 

 form-value of the whole ororanic individual is no lonofer that 

 of a true nucleated cell, but that of a non-nucleated cytod. 

 i.e. a simple protoplasmic body in which no true cell-kernel 

 (nucleus) is to be found. (Cf p. 120.) Even if, with Hert- 



