IV. i INITIAL STRUCTURE OF THE GERM 



253 



to which he has given the name of the diminution of the chromatin. 

 The middle parts of the chromosomes in somatic cells become 

 divided transversely into small granules, the ends remain rod- 

 shaped. The granules of the middle parts are alone divided and 

 pass to the daughter nuclei, 

 while the ends are cast out 

 into the cytoplasm and there 

 degenerate. The chromosomes 

 of the germ-cells (or of the 

 parent-cells of the germ-cells) 

 do not undergo this change, 

 but remain intact (Fig. 155). 



It might be argued that in 

 such a case as this the deter- 

 mination of certain characters 

 somatic is brought about 

 by the expulsion of the chro- 

 matin into the cytoplasm. 



5. A great deal of stress 

 has been laid on the impor- 

 tance of the experiment, due to 

 Boveri, in which the enucleate 

 fragment of the egg of one 

 species of sea-urchin gives rise, 

 when fertilized with the sperm 

 of another species, to a larva 

 which exhibits the characters 

 of the male parent alone. 



6 Boveri has brought for- same in Cucurl)itn P e P- c > root-hair 



VJ -U\J V Cl 1 11 tlo UL VJLili li U J.v/1. _ yt 7 _ j_l 1 i 



b oi Cannabts sativa : the nucleus is at 



ward evidence to show that the growing point. (After Haberlandt, 

 the abnormal development of from Korschelt and Heider.) 

 Echinoderm eggs which follows on polyspermy is in reality due 

 to the irregular distribution of the chromosomes to the daughter- 

 cells. Hence it is argued that the chromosomes are qualita- 

 tively different. 



These are the reasons which are, or have been, brought 

 forward in support of the belief that the nucleus is not insignifi- 

 cant in differentiation. We may now discuss them in order, 



ABC 



FIG. 153. A, origin of a root-hair 

 in Pisum sativum. The nucleus is 

 placed at the point of origin. B, the 



