STUDIES ON THE CELLS OF CATTLE. 3OI 



somes divide considerably in advance of the others. This point 

 was observed in several of the early metaphase stages; it was 

 fairly common in polar views of late metaphase stages, and in a 

 few instances a chromosome was found almost completely split 

 in two even in the late prophase. For this reason, in selecting 

 cells for accurate chromosome counts great care must be exercised 

 not to select polar views of late metaphase stages. The increase 

 in number may also be due to fragmentation, although one would 

 expect this only in poorly fixed material or general poor technique. 

 After the counts in the first one hundred camera-lucida sketches 

 showed that over ninety per cent, of the cells contained thirty- 

 seven chromosomes, no more sketches were made. However, 

 hundreds of other counts were made from favorable cells off-hand 

 with about the same results. This shows that in at least ninety 

 per cent, of the male somatic cells thirty-six ordinary chromo- 

 somes, and a single sex-chromosome were present. The ten 

 per cent, of discrepancies is undoubtedly due to unnatural states 

 and probable sources of error. The studies of the chromosomes 

 in the somatic cells of the female were conducted in the same 

 manner. Among the first one hundred cells, ninety-one showed 

 thirty-six ordinary chromosomes and two accessories. In several 

 hundred further counts, the percentage of discrepancies was 

 about the same. 



In the case of the six small embryos in which sex could not be 

 determined morphologically, or was uncertain, one was poorly 

 fixed, although it was cut into small pieces, and, therefore, could 

 not be used in this study. Of the other five two were unquestion- 

 ably female and three were male, according to evidences from the 

 cytological standpoint. In the case of the two specimens, cells 

 in various parts of the body repeatedly showed thirty-six ordinary 

 chromosomes and two accessories. In many instances where the 

 ordinary chromosomes could not be counted, the two sex chromo- 

 somes were recognizable. In the other three specimens the cells 

 invariably showed only a single sex-chromosome, and in many 

 cases the thirty-six ordinary chromosomes were counted. 



These extensive studies indicate quite conclusively that thirty- 

 six is the number of ordinary chromosomes in the somatic cells 

 of both sexes and that the male cells contain one sex-chromosome 



