118 bulletin: museum of comparative zoology. 



There* seems to be a great amount of disagreement as to just what 

 constitutes individuahty, but I beheve that we may class as instances 

 of individuahty all cases where it can be shown that the substance of 

 any telophase chromosome gives rise to one and only one prophase 

 chromosome. In that event, any one of the three theories mentioned 

 above would support the theory of individuality. I believe that I 

 have demonstrated individuality for chromosome-pair A, and have 

 shown good evidence for it among the other chromosomes of Phryno- 

 tettix. Besides, it seems to me much more logical to regard the con- 

 stant reappearance of the same architectural conditions of a given 

 chromosome as a result of continuity of that architecture in some 

 form or other through all the cell-divisions, than to assume that the 

 organization is entirely destroyed and reestablished between successive 

 mitoses. 



C. Chromosomes and Heredity. 



Any discussion of the relation of the chromosomes to heredity must 

 deal to a considerable extent with theory and speculation. Yet there 

 are many facts which tend to the belief that the chromosomes are, 

 after all, directly concerned with the transmission of hereditary 

 qualities. A few facts and some theory will be considered in the 

 following paragraphs under the two heads: — (a) Mendelism and 

 maturation, and (b) some experimental evidence. 



a. Mendelism and Maturation. 



Wilhelm Roux was apparently the first to formulate, in the early 

 eighties, a theory in which an attempt was made to localize the 

 carriers of hereditary qualities in the chromosomes; this was later 

 elaborated by others, especially by Weismann, who postulated a 

 reduction division which has since been identified with one or the 

 other of the maturation divisions. Montgomery ('01) pointed out 

 that the chromosomes of the diploid series occur in pairs, the members 

 of each pair being of the same shape and size. There are thus two 

 similar series of chromosomes. He concluded that one series was 

 derived from the maternal, the other from the paternal ancestor. He 

 concluded further that the members of each pair unite to form the 

 bivalent chromosomes of the first spermatocytes. Boveri ('02) de- 

 cided from the results of his experiments on dispermic echinoderm 



