THE GAMETES IN PLANTS AND ANIMALS 



327 



rate of metabolism and are not involved in the early differentiations, 

 but differentiate later. 



A recent study of modified cleavage made by Boveri ('10) on 

 polyspermic and centrifuged eggs of Ascaris has proved beyond a 

 doubt that the occurrence or non-occurrence of chromatin diminu- 

 tion in a nucleus depends, not upon its qualitative constitution, 

 but upon its cytoplasmic environment. If this is true, persistence 

 of the undiminished condition is not a segregation of preformed 

 germ plasm, but a nuclear reaction to cytoplasmic conditions. The 

 "germ path" is a feature of the cytoplasm, not of the nucleus, and 

 the cytoplasm is not, properly speaking, a part of the germ plasm 

 at all, but represents the soma of the cell. Which nuclei shall 



143 



Figs. 143, 144.— First and second division in egg of Cyclops, showing at one pole 

 of spindle the granules which mark, the germ path. From Amma, '11. 



become the nuclei of germ cells is determined, not primarily by 

 the nuclei themselves, but by the soma of the cell; the germ plasm 

 is not then an independent entity, but is determined by correlative 

 factors, like any other part of the organism, except the apical or 

 head region. 



Hacker ('97, '02) has described a germ path for Cyclops and other 

 copepod Crustacea, and his observations have been confirmed by 

 Amma ('11). The germ path in this case is characterized by cer- 

 tain granules which appear at one pole of the first cleavage spiniUe 

 (Fig. 143), pass into one of the two daughter cells, and later aggre- 

 gate into larger masses and disappear. At the second division 

 (Fig. 144) and also at the third and fourth divisions similar granules 



