260 A. RICHARDS. 



isolated, and have grown into small nuclei distinct from the 

 true nucleus of the cell. Such a case Boveri described for 

 Ascaris. Except in regard to size and the number of chromo- 

 somes entering into them, these smaller nuclei have the same 

 structure as those of regular types, and their membranes cannot 

 be distinguished from that of the larger nucleus. Boveri's 

 minute pathological nuclei are themselves an argument for the 

 view that the chromosomes retain their independence in the 

 normal completely fused nuclei which is usually described for 

 this form. In these hybrid fish eggs, fundamentally the same 

 condition obtains, for the vesicles, closely applied to each other 

 as they are, actually retain their identity, although no cyto- 

 plasmic layer intervenes between them. Vedjdowsky has 

 expressed a somewhat similar view in regard to the nuclear 

 membrane for he holds that it represents the peripheral portion 

 of the certain chromosomes that have become vacuolated in 

 their interior. 



Experimental vesiculation of chromosomes has not proven 

 difficult to bring about in cleaving eggs. Years ago Boveri 

 published the results on Ascaris eggs just mentioned, in which the 

 chromosomes may fail to fuse and each form its own nucleus- 

 like vesicle, and his observations have been repeatedly con- 

 firmed. Conklin's numerous experiments on Crepidula eggs ('12) 

 will suffice to show how common a phenomena vesiculation is. 

 By various means the chromosomes of the eggs were prevented 

 from fusing and each formed in the resting stage an independent 

 "karyomere" quite comparable to Boveri's cases. Other in- 

 stances might be cited. 



A phenomenon which may be so easily induced as this one is 

 most readily understood if one thinks of the normal nucleus in 

 interkinesis as consisting of closely crowded entities, the vesicles, 

 derived from the telophase chromosomes, which never normally 

 coalesce. This means that the unusual conditions of the experi- 

 ment merely push them a little apart from each other. As in 

 the case of a catalyzed reaction, a condition which already 

 exists may be modified easily, while it is very difficult indeed to 

 bring about an entirely new set of relationships between elements 

 not normally reacting. 



