GERM CELLS OF COELENTERATES 37 



of yolk. While growth begins before such bodies occur, the 

 period of rapid growth is coincident with the passage of nuclear 

 matter into the cytoplasm. The nucleolus is partly chromatic, 

 and the bodies in the cytoplasm derived from the nucleolus also 

 contain chromatin. Clava shows essentially the same phe- 

 nomena, but the chromatin which passes into the cytoplasm 

 appears earlier and comes from the nuclear reticulum, the 

 nucleolus being a true plasmosome. After the chromatin enters 

 the cytoplasm of Clava, growth begins. Growth begins in 

 Aglantha shortly before nuclear substances enter the egg, or at 

 least before definite cytoplasmic bodies can be recognized. In 

 this egg it is not possible to determine the fate of the chromatin 

 particles, except for their rapid solution within the cytoplasm, 

 nor whether they have any close relation to cell metabolism. In 

 the egg plasm of Hybocodon, chromatin granules appear before 

 the growth of the oocyte begins; this migration of chromatin is 

 abundant during early growth, but soon ceases, and the particles 

 dissolve wdthin the cytoplasm. Eudendrium shows similar in- 

 clusions in oocytes as growth begins, and they continue to form 

 abundantly during practically the whole of the growth period. 

 They are apparently of chromatic nature. 



The interpretation of these cytoplasmic inclusions involves, 

 chiefly, the consideration of their origin. Do such bodies arise, 

 in the place where they first appear, out of materials of the 

 cytoplasm, or do they represent nuclear substances in the 

 cytoplasm? If the latter be the case, are the bodies composed 

 of chromatin or of achromatic material? Bodies of cytoplasmic 

 origin have commonly been called mitochondria, those believed 

 to be chromatic in nature are sometimes referred to as chromidia. 

 Tests seem to have demonstrated the reality and difference of 

 these two classes of inclusions, for Cowdry ('16) believes, ''we 

 have ample evidence that the chromidial substance (Nissl sub- 

 stance) is a nucleoprotein containing iron . . . ., formed at 

 least in part through the activity of the nucleus, and the 

 mitochondria is a phospholipin albumin complex." 



The granulations in the egg cells of the described coelenterates 

 are certainly not mitochondria, though typical mitochondria 



