m'clung: cytology and taxonomy. 213 



exactly the same size, form and physical constitution, nor that 

 there is not addition to, or change in, the material substance 

 of which they are composed. They are no more' immutable or 

 invariable than the grasshopper which at one time is an egg, 

 at another a nymph, and finally a full-winged adult. I would 

 as soon question the individuality of one as of the other, on the 

 argument that they cannot always be distinguished in the same 

 form. Enough evidence has now been developed by various 

 cytological and experimental researches to show that there is a 

 fixity and definiteness in chromosome organization sufficient to 

 support adequately what is commonly known as the theory of 

 the "individuality of the chromosomes." The burden of proof 

 rests strongly upon those who oppose this theory, and to re- 

 move it they will have to offer some definite explanation for 

 the appearance of such a structure as the hexad multiple of 

 Hesperotettix. 



The mere fact that the chromatin granules diffuse through 

 the nucleus so that the outlines of the individual chromosomes 

 cannot be distinguished is no argument against the persistence 

 of the chromosomes. Neither can I regard the occurrence of 

 occasional cases of amitosis as in the least weakening the 

 theory of chromosome individuality. It may teach us more 

 about chromosomes to learn that under some circumstances 

 they may show such a suspension of visible integration as ami- 

 tosis would indicate, but we shall first have to know a great 

 deal more about amitosis than we do now, and we shall want to 

 know how much the parasitical nature of the forms in which 

 direct division usually occurs has had to do with the modifica- 

 tion of all other organic phenomena. In other words, I main- 

 tain that other than negative evidence will have to be offered 

 in explanation of the occurrence of the same number of chro- 

 mosomes throughout the family Acrididae, and of the same 

 combination that characterizes certain genera. If these are 

 not self-perpetuating structures then there is some agent out- 

 side which determines their being, and it will be necessary to 

 demonstrate this before the simpler self-integration theory is 

 abandoned. 



I am quite prepared to admit also that in one species even 

 there may be a variation in the integration of the chromatin 

 material, resulting in some numerical variation of the chromo- 

 somes, without losing my belief in the necessity for this defi- 



2-Univ. Sci. Bull., Vol. IV, No. 7. 



