No. 535] GERM-CELL DETERMINANTS 



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question. This theory holds that the chromatin of the 

 germ cells is of two kinds— (1) idiochromatin, which is 

 for reproductive purposes, and (2) trophochromatin 

 which performs vegetative functions. In many Protozoa 

 these two kinds of chromatin are separate throughout 

 the life cycle. For example, in Paramecium the micro- 

 nucleus is thought to represent the idiochromatin, the 

 macronucleus, the trophochromatin (Calkins, '09). Dur- 

 ing conjugation and the subsequent reorganization of the 

 nuclear apparatus the macronucleus breaks down and 

 disappears, whereas the micronucleus gives rise not only 

 to new bodies like itself, but also to new macronuclei. 



In most animals idiochromatin and trophochromatin 

 are supposed to be contained in one nucleus and are in- 

 distinguishable except in a few cases during the differ- 

 entiation of the germ cells at an early developmental 

 period of the egg. One is tempted to interpret as idio- 

 chromatin (1) that part of the chromosomes of Ascaris 

 which is lost by the somatic cells (Fig. l,B,c) but retained 

 by the germ cells, (2) the nuclear material which is pres- 

 ent in the primordial germ cell of Cyclops (Fig. 2, B, ak) 

 but is absent from the somatic cells, (3) the similar sub- 

 stance in the primordial germ cells of Oophthora (Fig. 

 4, n), (4) the "besondere korper" in the egg of Sagitta 

 (Fig. 3, a), and (5) the pole disc in the eggs of chryso- 

 melid beetles (Fig. 5, A, gc.d). 



One difference between these substances and the germ 

 plasm as Weismann conceives it should be pointed out. 

 In the cases cited above the material interpreted as germ 

 plasm is only in one instance chromatin, and in this 

 animal (Ascaris) it does not constitute the entire chro- 

 matin as Weismann 's theory demands. If these extra 

 nuclear bodies really represent the iodioplasm our loca- 

 tion of the germ plasm must be transferred from the 



