l88 J. S. NICHOLAS 



large units whose extrinsic relations are engaging attention, and in the 

 main they are paying little heed to those intrinsic cellular relations 

 which must be of such dominant import in the final extrinsic reactions 

 which are formative of the patterns through which the organizational 

 structural relationships arise. 



The unitary influence of cytoplasm and nucleus in the initiation of 

 cell division was a moot question at the beginning of the century. Since 

 in some of the determinant forms the first division coincides with the 

 later axial relations the problem of nuclear or cytoplasmic dominance 

 in the activation of the primary division becomes a rather vital ques- 

 tion. It is clearly recognized today that normally there is an interacting 

 significance of each of these parts in which certain components are 

 actively engaged, but that experimentally there are multiple mechanisms 

 for attainment of the result. 



The Problem of Nucleo-cytoplasmic Relationships 



In the sea urchin Boveri ('07) has shown that so long as the chromo- 

 somal complex of the egg contained a normal complement of chro- 

 mosomal material development proceeded regularly. Double or half of 

 the normal series might be represented, the quantity apparently having 

 little significance so long as the quality of each of the constituent 

 chromosomes was present. Baltzer ('40) and Hadorn ('36) have been 

 able to eliminate the action of the female pronucleus and consider only 

 the reaction of the paternal pronucleus with reference to egg develop- 

 ment. Complete development has been attained, as would be expected 

 from some of the preceding results with invertebrate eggs. Conklin 

 ('31) on the basis of much work has decided that the cytoplasm has a 

 very complex and interesting role in the process of development; his 

 results were indicative of the fact that the cytoplasm itself was prob- 

 ably of a greater independent activity than hitherto suspected. Fank- 

 hauser ('34) in his study of the polyploidy has likewise shown quanti- 

 tatively that the influence of the nucleus must be regarded as being 

 comparatively negligible upon the total process of differentiation. 



E. B. Harvey ('36 and '46) has made an interesting series of studies 

 upon the Arbacia egg. She has employed centrifugation in separating 

 the uncleaved egg into four parts in each of which the constituents 

 separate regularly. After the process of separation is complete, the 

 fragments are activated parthenogenetically. Subsequent cell cleavage 

 takes place and may proceed to the formation of as many as 500 cells ; 



