30 Hyhridization of Echinoids. 



nuclei. It is clear that cytoplasmic differences must be taken into 

 account. The life of the cell lies in the interaction between nucleus 

 and cytoplasm. The relative importance of each is that of enzyme 

 to substrate. There can not be cytoplasmic control, nor can there 

 be nuclear control, purely as such, for the processes of life lie in the 

 interaction of both. There is nuclear control in that by the intro- 

 duction of enzymes we obtain synthetic products; there is cytoplasmic 

 control in that with a given substrate we provide material from which 

 products are synthesized. 



From the evidence given by Arbacia-Moira material (Tennent, 

 1920), it seems clear that the reactions in the cytoplasm caused by 

 foreign sperms are unlike the reactions caused by species sperms. 

 That fact fixes the attention on the nature of the activities of the 



nucleus. 



The Binuclearity Hypothesis. 



Various binuclearity hypotheses, founded in part on Richard 

 Hertwig's chromidial hypothesis, have influenced interpretations of 

 nuclear phenomena. The nucleus shows two phases, an active and 

 a resting. These two phases, kinetic and interkinetic, have been 

 made to lend themselves to an analogy with a true binucleate con- 

 dition and to an assumption of dichromaticity. Of these two kinds 

 of chromatin, one is supposed to be propagatory (idiochromatin), 

 in evidence at the time of cell division; the other trophic (tropho- 

 chromatin, somatochromatin), formed by the idiochromatin, but 

 resident in the cytoplasm. The somatic phase of the nucleus covers 

 a period during which it may be assumed that nuclear enzymes 

 have passed from the nucleus into the cytoplasm, and the cytoplasm 

 has become the seat of synthetic activities. The nucleus at this time 

 is in a ''resting" condition; it seems comparatively empty, is acido- 

 phile, and basophilic bodies may be found in the cytoplasm. Under 

 the influence of the chromidial hypothesis, supposed particles of 

 chromatin in the cytoplasm have been interpreted as chromidia, or 

 as trophochromidia. The basophilic bodies found in cross-activated 

 Arhacia eggs might have been interpreted similarly had there been 

 any evidence that they were emitted from the nucleus. The possi- 

 bility of the emission of large particles is foreign to our conception 

 of the nature of the nuclear membrane. 



