350 KANSAS UNIVERSITY SCIENCE BULLETIN. 



upon the actuality of the phenomena upon which such inter- 

 pretations are based. 



Fundamentally, these disagreements concern more or less 

 intimately that view of chromosome organization which is 

 called the "theory of chromosome individuality." Modem 

 cytologists are either supporters or opponents of this theory, 

 and its adequacy or inadequacy will be determined by the 

 weight of evidence now accumulating. It is, of course, im- 

 possible to conceive that it will stand unmodified, for it is but 

 the expression of our present limited knowledge; but it must 

 now be determined whether these structures of the cell have 

 persistent individualities or whether they are merely incidental 

 and inconstant expressions of more fundamental phenomena. 

 Observed facts must support one or the other of these alterna- 

 tives, although in doing so they may readily enough modify 

 the established order. 



A considerable body of evidence has accumulated within re- 

 cent years to support the theory of chromosome individuality 

 and to associate the development of sexual characters with 

 particular chromosomes. To this has been added the support 

 of experimental work on sex determination and the parallel- 

 ism between the segregation of Mendelian characters and the 

 behavior of the chromosomes in the maturation divisions of 

 the germ cells. Much of this cytological work has been done 

 upon the insects, particularly in the orders Orthoptera and 

 Hemiptera, and, in the large, there is a strong consensus of 

 opinion. More recently confirmatory evidence has been fur- 

 nished from studies upon nematodes, including Ascaris, by 

 Boveri, upon echinoderms by Baltzer, and upon birds and man 

 by Guyer. Here and there, however, there are workers who 

 question the fundamental facts and deny the correctness of the 

 theories founded upon them. 



It is necessary, in order to proceed further with our inter- 

 pretations, that we reach an agreement upon the observable 

 facts in our science, and no honest question should remain 

 without answer. 



At present one of the most serious diversities of opinion 

 exists regarding the character and the behavior of the acces- 

 sory chromosome in the bug Anasa tristis. Because of the ex- 

 tensive and painstaking studies of hemipteran germ cells by 

 Wilson, the contradictions and inaccuracies in the studies of 



