266 BERTRAM G. SMITH. 



entities whether visibly separated or not. The distinction be- 

 tween the two classes of germ-nuclei those that fuse at the 

 time of fertilization and those that do not is more apparent 

 than real. The expression "individuality of the germ-nuclei" 

 seems justified in either case, for individuality implies separable- 

 ness as well as separateness (Conklin, 1916); but some may 

 prefer to use the term "autonomy," which places the emphasis 

 upon independence. Since attention has become focused upon 

 the chromosomes, the expression "autonomy of the maternal 

 and paternal chromosome groups" has often been used to indicate 

 the duality of nuclear structure. 



Where it exists, the separation of maternal and paternal chro- 

 matin-complexes into distinct groups within a single nucleus 

 affords a striking exemplification of the deeper and more uni- 

 versal truth that each germ-nucleus is represented in its entirety 

 in every cell, somatic as well as germinal, of a developing organ- 

 ism. In Cryptobranchus allegheniensis this dual structure of the 

 nucleus is clearly visible in every cell of the early segmentation 

 stages at least, so that here we have material for an ocular 

 demonstration of a principle long ago foreseen by Huxley (1878), 

 who wrote: "It is conceivable, and indeed probable, that every 

 part of the adult contains molecules derived from both the male 

 and the female parent; and that, regarded as a mass of molecules, 

 the entire organism may be compared to a web of which the 

 warp is derived from the female and the woof from the male." 



SUMMARY. 



In the fertilization of the egg of Cryptobranchus allegheniensis 

 the germ-nuclei do not fuse, and in the first cleavage mitosis each 

 gives rise to a separate group of chromosomes whose descendants 

 pass separately to the daughter-nuclei. 



During the ensuing resting stage each germ-nucleus is repre- 

 sented by a structurally distinct vesicle. The separateness of 

 the germ-nuclei is thus maintained throughout the entire nuclear 

 cycle. 



Throughout early cleavage the nuclear divisions are of the 

 same duplex type, and the resting nuclei are always distinctly 



