170 ROBERT T. HANCE 



cerned, like normal spermatogonial cells. The other possibility 

 is that the chromosomes in the somatic cells have fragmented. 

 This suggested itself to me particularly, as I had discovered that 

 the variation in the number of somatic chromosomes in the 

 evening primrose, Oenothera scintillans, is due to the fragmen- 

 tation of certain chromosomes (Hance, '18). In the case of 

 Oenothera scintillans I found the chromosomes showing deep 

 constrictions which led to the solution of the problem in this in- 

 stance. The conditions in 0. scintillans will be discussed later. 

 Although I have searched for such constrictions in the chromo- 

 somes of the pig, I have never found any of which I could be 

 certain. In several cases chromosomes have been found in 

 which there appeared to be a constriction but this interpretation 

 was always open to considerable doubt. In figiu-e 36, to the left 

 of the number is one of the best cases of a thin area in a chromo- 

 some that I have found. One of the chromosomes in figure 85 

 also shows constrictions. When a large number of chromosomes 

 are concerned, it becomes a matter of considerable difficulty to 

 determine whether a chromosome has been found showing a con- 

 striction or whether this dent is really due to the overlapping or 

 approximation of two chromosomes. Although it has been im- 

 possible actually to demonstrate the possibility of fragmentation 

 through the discovery of constrictions in the chromosomes, there 

 are, however, indirect methods of proving that this process is 

 going on in the pig. If the chromosomes are breaking up we 

 would expect to find, as in the case of Oenothera scintillans, 

 that those cells showing a high degree of fragmentation would 

 give ocular evidence of the fact by possessing visibly shorter 

 chromosomes. Those cells which possess only a few more than 

 the spermatogonial number of chromosomes should appear like 

 the germ cells, while those having forty-five or more should have 

 chromosomes which are obviously shorter. A comparison of a 

 cell having many chromosomes with others in the same tissue, 

 or in other tissues having the spermatogonial number or very close 

 to it, will show that the chromatin bodies in the many-chromo- 

 some cells are in general, shorter. Compare figures 23 to 80 with 

 figures 1 to 20 and the photomicrographs 96, 97 and 98 with 99. 



