THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 183 



minimum lengths found for the spermatogonia! chromosomes. 

 One cell enters within the spermatogonia! minimum curve at 

 chromosome 3 and continues, either on it or very close to it, 

 for a considerable distance. This, however, is a 'longer' cell 

 than the other two and would be expected to rise above the 

 type minimum more quickly than the others. It does not, Imw- 

 ever, rise noticeably above the minimum curve at the long end of 

 the series, notwithstanding its extra total length. The other two 

 curves do not rise above the minimum curve until chromosome 

 27 is reached. These three cases, which are typical for others, 

 most certainly show that the chromosomes at the long end of the 

 series have been reduced considerably in length. This becomes 

 especially clear when the broken lines in text figure 3 are followed 

 and contrasted with the results mentioned above. These 

 curves represent one cell with unfragmented chromosomes and 

 another in which there is a single fragment. The curves lie 

 within the extremes of the spermatogonial lengths for the full 

 distance, and the curve representing the chromosomes of the 

 unfragmented cell coincides with the spermatogonial average 

 curve for a great part of its length. 



Hence it seems entirely justifiable to claim that, although the 

 exact chromosomes which have broken up cannot be ascertained, 

 as was done in the case of Oenothera scintillans, the same gen- 

 eral conditions hold true, namely, that the chromosomes of the 

 long end of the series have fragmented. This, of course, does not 

 exclude the possibility that some of the shorter chromosomes 

 have broken up. Since this was discovered in Oenothera scin- 

 tillans, and since the other conditions in both forms are so com- 

 parable, it seems probable that the fragmenting of some of the 

 shorter chromosomes may occur in the pig. Neither has it 

 been possible to show that a chromosome has not lost more 

 than one piece. For various reasons, however, I am, at present, 

 inclined to think that a chromosome does not lose more than 

 one piece or, if it does, that the condition is rare. 



The point of fragmentation. That the fragments should be so 

 nearly of even length in the two forms studied is very suggestive, 

 and would seem to indicate that one or two chromomeres have 



