GERM CELLS OF COELENTERATES 91 



as the egg approached inatiirit}^" This pigment was found to 

 show first about the nucleus and later to spread throughout the 

 egg; the pigmentation was correlated with yolk formation in 

 some way. The present study has demonstrated the liberation 

 of substances from the nucleus and has established the fact that 

 this is coincident with the formation of yolk. This is in exact 

 harmony with, and explanatory of, the observations on the for- 

 mation of yolk in the living egg. Such an agreement of living 

 behavior with inferences from cytological investigations would 

 seem to warrant the conclusion that the morphological structures 

 found in sections are in no measure artifacts, but are normal. 

 Also the conclusion is rendered undoubted that such structures 

 (referred to as chromidia, extra-nuclear chromatin, etc.) are in 

 reality of nuclear origin. This latter point has been doubted 

 by some and recently Beckwith ('14) has said that such particles 

 are not chromatin and do not come from the nucleus but arise 

 in the cytoplasm de novo. This point I shall discuss more fully 

 later, but here I desire to call attention to the confirmation from 

 living eggs of the nuclear origin of substances which condition 

 yolk formation within the egg. 



The conditions are then essentially alike in the campanularian 

 hydroid, Campanularia, and the tubularian hydroid, Clava. 

 There is the difi'erence that in the former the nucleolus played 

 an important part and in Clava this is apparently not the case. 

 The only indication of activity in the nucleolus of Clava is in 

 the vacuolation (figs. 5 to 9) ; there is none of the subdivision and 

 gradual dissolution so characteristic of Campanularia. Corre- 

 lated with this difference in behavior is the fact that the nucleolus 

 of Campanularia contains much chromatin, while in Clava it 

 appears to be a real plasmasome, almost if not entirelj" devoid 

 of chromatin. A still further correlation lies in the presence of 

 an extremely delicate, fine meshed, faintly staining reticulum 

 in the nucleus of Campanularia, and a deeper staining, coarsely 

 granular and wide meshed reticulum in Clava. The chromatin 

 of the nucleus appears to be the dynamic center and, if this 

 be located in the nucleolus, the latter may function actively, 

 but if the nucleolus be devoid of chromatin, it seems to have a 



