THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 171 



With the ocular evidence in favor of the breaking up of the 

 somatic chromosomes, further evidence indicating that such a 

 process is actually taking place may be offered. That the 'extra ' 

 chromosomes divide and behave normally has been described 

 above. They are not as a rule at least, lost from .the complex. 

 If the extra chromatin bodies present are not due to additions 

 to the regular nuclear equipment, but rather to the breaking up 

 of the type chromosomes, the total length of all of the chromo- 

 somes in any somatic or spermatogonial cell, regardless of the 

 number of separate elements possessed, should be approximately 

 the same. The results of an investigation to determine this 

 point follow. 



THE METRIC ANALYSIS OF THE CHROMOSOMES 



In studying the chromosomes, use has been made of the method 

 first developed in the work on the evening primrose, Oenothera 

 (Hance, '18). Measurements of chromosomes have been made 

 before, but the discovery of the exact inter-pair relationship is, 

 in somatic cells as far as I am aware, new, and should prove of 

 considerable value in studying cytological data (particularly in 

 the determination of the chromosomes involved where irregu- 

 larities occur) . Since these methods were worked out I find that 

 Robertson ('15) has employed the relationship of certain chromo- 

 somes expressed in ratios in some of his Orthopteran studies. 

 This will be referred to in the discussion. Sutton ('02) was the 

 first to determine the paired condition of the germinal chromo- 

 somes. He pointed out that the pairs differed in length and 

 maintained a definite and constant size from one cell generation 

 to another, and also that the pairs, when arranged according to 

 length formed a practically uniformly graded series. Meek ('12a, 

 '12b and '15) has also made extensive measurements. These 

 methods permit the accurate checking of results and eliminate, 

 to a large degree, the personal element which so frequently en- 

 ters cytological work. Relationships not optically discernible 

 are brought out, and the application of the method to the work 

 of others enables an investigator to check his work as regards 

 accuracy and interpretations. 



