THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 181 



8. Fragmentation does not affect the germinal chromosomes. 



A comparison of the conditions in the two forms. When the 

 summary of the observations on the pig is compared with the 

 preceding one on Oenothera scintillans it is plain that, with one 

 or two exceptions, the words pig and Oenothera could be in- 

 terchanged without affecting the truth of the statements in the 

 slightest. The relationship between the pairs differs slightly, 

 but is, however, fairly constant in both species. The chief 

 discovery in the case of the Oenothera is that it is possible to 

 reunite the fragmented chromosomes and thus determine, with 

 a fair degree of accuracy, which chromosomes have broken up. 

 Is this method of procedure applicable to the chromosomes of 

 the pig? Can the chromosomes which have fragmented be 

 located? The chance of even approximate accuracy in attempt- 

 ing to reunite the fragmented chromosomes of the pig is so 

 slight that it would be unwise to base any conclusions on the 

 results. This is true for the following reasons: 1) The large 

 number of chromosomes and the consequent and very probable 

 slight inaccuracies in drawing are prohibitive of the success of 

 such a study. 2) The very slight differences, in the majority of 

 instances, between the chromosome pairs present no definite 

 criterion on which to base judgment as to which chromosomes 

 are out of place in the series and consequently with which 

 fragments they should be united. 



It is possible, in a more direct way, however, to determine 

 which chromosomes of the series are breaking up. The method 

 is not so completely satisfactory as the one used with the evening 

 primrose, but serves to show, in a general way and with a con- 

 siderable degree of accuracy, which end of the chromosome 

 series is breaking up. In plate 9 it will be recognized at once 

 that, in general, in those somatic cells (row 3 to 12) possessing a 

 large number of chromosomes, the chromosomes at the begin- 

 ning of the series are shorter than the chromosomes of the 

 spermatogonium (row 1) and of the unfragmented brain cell 

 (row 2) in the same columns. There are exceptions to this 

 which tend to sljow that, in breaking up, the chromosomes 

 may not follow a definite plan beginning with the long chromo- 



