468 HOPE HIBBARD 



cell and to trace the interrelations of distinct bodies through 

 different stages. The possible transformation of mitochondria 

 into secretion granules, pigment, yolk, etc. (Cowdry gives a 

 list of eighty such things into which mitochondria have been 

 reported to change), and the cycle described by Schreiner ('15), 

 in which fragments of the nucleolus wander into the cytoplasm, 

 unite into vegetative threads, and break up into secondary 

 granules which are ultimately transformed into fat drops, are 

 instances of these attempts to consider visible structures as 

 steps in the physiological processes of the cell. 



The processes of metabolism in the cell necessarily include ac- 

 tivities of both nucleus and cytoplasm. The part played by the 

 nucleus is not fully understood. Some investigators have de- 

 scribed particles of material passing out of the nucleus into the 

 cytoplasm. These particles have been regarded as chromatin 

 (Schaxel, '11; Danchakoff, '16), or as fragments of the nucleolus 

 (Schreiner, '15; Nakahara, '17; Walker and Tozer, '09; Har- 

 gitt, '19, etc.). According to other investigators, the nucleus acts 

 on the cytoplasmic substrate by liberating enzymes, which 

 diffuse through the nuclear membrane and permeate the cyto- 

 plasm. Tennent ('20) has found in Arbacia eggs fertiHzed by 

 Moira sperm, precipitates in the cytoplasm which are interpreted 

 as the result of enzymes from the nucleus brought in by the 

 foreign sperm. 



The present work was undertaken in the hope of demonstrat- 

 ing more exactly the relation between the nucleus and the cyto- 

 plasm by comparing the cytoplasmic contents of an egg fertiHzed 

 by sperm of its own species with that of an egg fertiHzed by 

 sperm of another species. It was thought possible that the cyto- 

 plasm when acted on by two different types of nuclear enzymes 

 might show visible differences. In the study of the particular 

 cross made, Echinarachnius X Arbacia, no such visible differences 

 between the self-fertilized and the cross-fertiHzed eggs have been 

 found. This does not invaHdate the conclusion that the nucleus 

 gives out enzymes into the cytoplasm. It probably indicates 

 that in the particular cross used here the enzymes of the foreign 

 sperm were so much like those of the species sperm that no 



