CAUSES OF STERILITY IN THE MULE. 33 



this stage (Fig. 7). The abnormality appears to have taken 

 place in the last two divisions of a spermatogonial cell ; only the 

 nuclei have divided and therefore remained in the same mass of 

 cytoplasm. Primary spermatocytes with four nuclei appear 

 occasionally, but in practically all cases there is evidence that 

 the abnormality had occurred within the cells themselves and 

 not in the spermatogonia. 



Fig. 39 is another giant cell in which all of the chromosomes 

 seem to be in the huge non-symmetrical quadripolar spindle. 

 About a hundred chromosomes could be counted in this cell, 

 some of which are apparently the result of division and others are 

 in the process of dividing. There are undoubtedly many more 

 chromosomes present but the exact number could not be de- 

 termined owing to the position of the large equatorial plate. It 

 is probably a spermatogonial cell which possessed two complete 

 nuclei and the number of chromosomes in excess of one hundred 

 and two may be due to the fact that many of the chromosomes 

 have divided. Parts of the spindle seem to be in the late meta- 

 phase and others in the anaphase stage. 



MULTINUCLEATE CELLS. 



Primary spermatocytes with nuclei ranging from two to six 

 in number are not uncommon (Figs. 40-43). The most common 

 ones are those with two and four nuclei. Such cells appear to be 

 in the late telophase stage. There is much irregularity in size 

 among the nuclei of the same cell. For example, when two 

 nuclei are present they are sometimes of similar size and then 

 again one is much larger than the other. In cases where three 

 nuclei are present they are sometimes of practically the same size, 

 or form a gradation in sizes, or two large and a small one, or two 

 small and a large one appear, and so on. Frequently one or 

 more chromosomes were left in the cytoplasm while the others 

 formed one or more nuclei. Fig. 41 shows a decaying cell with 

 two nuclei, and a large chromosome left in the cytoplasm but 

 connected with one of the nuclei by a coarse strand. Such 

 strands were not always present. It is possible that the chro- 

 mosome in question is the accessory, though one of the chro- 

 mosomes within the nucleus to the left also resembles it. 



