34 W. E. HOY, JR. 



demonstrated in the various tissues of developing embryos. 

 From a comparison of the diploid groups in spermatogonia and 

 of those in oogonia, together with the haploid groups, which 

 have been described by Wilson and Morrill, it is clearly evident 

 that the members of these pairs of chromosomes are derived 

 one from the male parent and one from the female parent. 



Though the same size relations seen in the chromosome complex 

 of the germ cells is reproduced in the somatic cells, there is a 

 difference in size and volume of the homologous pairs in different 

 cells. This difference can probably be explained upon the 

 grounds of a greater or less metabolic activity of the nucleus; 

 that is, difference in size may be due to a real increase in the 

 amount of the chromatin. On the other hand it may be due 

 merely to the swelling of the chromosomes by absorption. 

 Conklin ('12) found that "the chromosomes of the spermatid 

 are usually smaller than those of the ootid, but when the chromo- 

 somes of the first cleavage spindle appear, those from the sperm 

 nucleus are usually as large as those from the egg. The reason 

 for this is to be found in the fact that both grow, after fertiliza- 

 tion, in the same medium, the egg plasma, and for approximately 

 the same length of time." He found that the size of the chromo- 

 somes is dependent upon the size of the nucleus from which it 

 comes, and that in general the small nuclei gave rise to chromo- 

 somes smaller in size than those which came from a large nucleus. 



So far as has been determined, none of the chromosomes in 

 the somatic cells are distinguished by any peculiar behavior. 

 All the chromosomes seem to divide at about the same time, 

 and in the same manner. The division plane is a longitudinal 

 one, separating the chromosomes into morphological identical 

 halves, as can be demonstrated in polar views of anaphases. 

 In some cases the individuals of a pair lie very close together, 

 but this is an extremely inconstant feature. Beyond a difference 

 in size it is usually impossible to distinguish various chromo- 

 somes by any peculiarity of shape, since the same pair may 

 appear U-shaped, slightly curved, or as straight rods in different 

 cells, and one chromosome of a pair may even differ very much 

 in shape from its mate. This is probably due to the position of 

 the particular chromosome in the equatorial plate, and to some 

 difference in tension of the spindle fibers. 



