THE DIPLOID CHROMOSOME COMPLEXES OF THE PIG 157 



they compare favorably in every way with those obtained on the 

 grasshoppers, the fixed tissue of which has been compared and 

 checked with studies on hving cells. The methods of fixation 

 which have been developed may now be said to place mammalian 

 tissues in the list of workable cytological materials. Probably 

 not the least of the reasons for the few ventures in to the field of 

 somatic cytology has been a scarcity of divisions, but this is an 

 avoidable condition for tissues may be found showing as many 

 mitotic figures as the best testicular material. The difficulty 

 that investigators frequently met with in locating dividing cells in 

 mammalian testes is entirely obviated by securing material from 

 several animals and then selecting for study that animal which 

 is in what I have termed elsewhere, a ' cycle of division. ' The 

 cycle holds for both testes and embryo, and I have found it 

 also in plants. 



Cytologists, who have studied the cells of the soma, may be 

 be divided into two general groups — those who maintain that the 

 somatic chromosome number is fixed and identical with that of 

 the spermatogonia, and those who belie^^e that it is variable. I 

 believe that it may safely be said that both groups have drawn 

 conclusions from too little evidence and, in some cases at least, 

 this evidence has been obtained from very poor material. This is 

 particularly true of the 'variable chromosome group,' among 

 whom belong those, who, with Delia \^alle, hold the chromosomes 

 to be unimportant structures and who believe that the supposed 

 variations express and emphasize the lack of chromosome im- 

 portance. WTiich of these groups is right will be considered later. 

 Ina recent paper (Hance T8) it has been pointed out that 



only when the investigator of somatic chromosomes has a sufficiently 

 large and properly preserved number of somatic figures to study and 

 hafe sul)jected the chromosomes to every possible analysis is he justi- 

 fied in taking up the cudgels for or against the theories that have de- 

 veloped around the man}'- excellent studies on germinal complexes. 

 There is a ver\' apparent and regrettable tendency of late on the 

 part of some cytologists to attempt merely to correlate their own 

 findings with those of some classic work on another form, passing, at 

 times, variations that have been found, either because they were thought 

 unimportant, because the}' were supposedly pathological, or perhaps. 



