MULTIPLE CHROMOSOMES 585 



these substances may be responsible for the integration of the 

 chromosomes, but it is the fact that there is a definite structure 

 to be identified which concerns us most. The substances of the 

 chromosome divide into new units of similar relative sizes, and 

 these structures, now of half the original content, take up unlike 

 materials and replace the missing portions. The complexes of 

 the daughter cells are now equivalent to that of the mother 

 unit. It is obvious that, since the chromosomes, as such, divide, 

 all of their substances must be involved. There may be some 

 question whether one may be lost as a morphological entity 

 while another persists — although this is much open to question 

 — but something maintains the organization which we recognize 

 in the chromosome and it is this organization which we study. 

 In view of the fact that our microchemical tests are so far from 

 specific in their action, it is not the part of wisdom to build very 

 extensive theories upon their evidence. It is quite possible that 

 one substance, in different phases of its activity, may present 

 alternately the aspects of chromatin and achromatin, and some 

 conditions of the staining reaction suggest this, so that it would 

 be unwise to involve the whole question of chromosome organi- 

 zation in a dispute regarding the nature of their substance, 

 based merely upon uncertain staining reactions. 



8. Chromosome specificity 



That chromosomes might be genetically continuous and still 

 be of the same nature, without differential character, is, of course, 

 conceivable. In fact it is more than probable that, in a sense, 

 they are all alike, for they probably share the general properties 

 or functions of protoplasm. But that they carry out these acti\d- 

 ties in the same manner is a conclusion quite foreign to the evi- 

 dence. Just what the nature of this differential action may be 

 has not yet been discovered, but the action of the sex determin- 

 ing chromosome and the groupings of characters in Drosophila 

 are suggestive. Male and female possess the same series of 

 parts, and the difference between them is one of relative develop- 

 ment. Nothing unique for either sex exists and such a thing 



