THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 169 



shows at least forty-three chromosomes. There are very Ukely 

 more present, but forty-three chromosomes were readily dis- 

 cernible. At the lower pole only thirty-six chromosomes were 

 distinguishable, but the spindle axis was slightly oblique to a 

 perfect polar view and consequently it was impossible, even to 

 approximate the actual number of chromosomes present. It is 

 evident in one case, at least, that the 'extra' chromosomes 

 behave as do the others and divide regularly. It is rarely that 

 I have found a cell in anaphase with the chromosomes trailing on 

 the spindle after the others had reached the poles as might be 

 expected if these ' extra ' bodies were eliminated. Figures 86 and 

 88 are thought to be two such cells. In figure 86 there is an area 

 surrounding a trailing chromosome that is lighter in color than the 

 cytoplasm and which appears as the beginning of a vesicle. 

 This vesicle might cause the disintegration of this chromosome 

 outside of the nucleus. The evidence for this, however, is very 

 poor. Evidence from another form on the constancy of the com- 

 plex will be mentioned presently in support of the above state- 

 ments. 



The cause of the variation in number 



Since the chromosomes of the male germ cells are con- 

 stantly forty in number, how has the soma acquired the wide 

 range of number that has been described? One explanation 

 would suggest that they are giant cells, or perhaps what may be 

 termed partial giants, due to the division, but lack of separation 

 of certain chromosomes, as found by Dr. Caroline Holt ('17) in 

 the cast off lining of the intestinal wall in Culex pipiens. This 

 is not likely for several reasons. In the first place the multiple 

 chromosome cells in Culex are degenerating and abnormal, while 

 the cells in the pig which show variation in chromosome number 

 are perfectly normal in appearance and size, and are part of ac- 

 tive, healthily growing tissue. When the somatic cells are com- 

 pared with the giant spermatogonium reproduced as figure 14, 

 it is very obvious that the cells of the soma are much smaller 

 and appear, so far as the diameter of the metaphase plate is con- 



