THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 



167 



nitely, I have counted the doubtful element as one rather than 

 two. This difficulty was encountered, particularly in cells pos- 

 sessing fifty or more chromosomes and, in many instances, cells 

 which I have placed in, for example, the fifty chromosome class 

 may well have fifty-one, fifty-two or fifty-three chromosomes. 

 There are certainly, however, at least as many chromosomes in 

 a cell as are indicated by my numbers and my drawings. 



Text fig. 1 A frequency curve (heavy band) showing the group distribution 

 of cells possessing various numbers of chromosomes as found in ninety-two 

 somatic cells of the pig. The thin solid line represents the range and distribution 

 of variation for cells of the brain and the broken line does the same for the 

 blood. None of these curves appear to have a definite mode. The number of 

 chromosomes are listed on the base line while the frequencies are recorded on the 

 axis of ordinates. 



The chromosome number in uncut membranes 



Since the main work of this study was completed I have ob- 

 tained fresh material from Cincinnati. The amnion of embryo 

 pigs (18 to 20 mm.) was prepared as described (page 160) and 

 was found exceedingly favorable for study. The thickness varies 

 but in the portions observed it was seldom more than three cells 

 thick and frequently the membrane seemed to be composed of a 

 single layer. The certainty that the cells were uncut made the 



