194 ROBERT T. HANCE 



fear, progressed very far toward the solution of the problem, but 

 several points have been developed which are of some interest 

 and may form a basis for future work along these lines. The 

 fact that the chromosomes may fragment in the soma has been 

 shown to be meaningless, so far as disturbing the quantity of 

 chromatin is concerned, in both the pig and Oenothera scin- 

 tillans. A definite and apparently constant relation between 

 the chromosome pairs has been discovered which will be of 

 great value in anah'sing unusual chromosome conditions, such 

 as fragmentation, multiple chromosomes, and the total loss of 

 parts of chromosomes. 



Contrasted to the breaking up of chromosomes we have the 

 fusion of certain elements, as described by McClung ('17), Rob- 

 ertson ('16) and Woolsey ('15) and the loss of a portion of 

 certain chromosomes: Carothers ('13 and '17), Robertson ('15) 

 and Wenrich ('16). In these cases the chromosome phenomena 

 hnk up closeh' with the taxonomic pecuharities. With the ex- 

 ception of those cases in which certain chromosomes are deficient, 

 the total length of the chromosomes of the cells where these 

 other phenomena have occurred, is, as expected, the same as in 

 the cases where the chromosomes have not fused. The fusion 

 has come about simply av^ an end to end union. WTiat these 

 phenomena may mean or how or why they have occurred is as 

 much of a riddle as is the breaking up of chromosomes. 



A great mass of unquestionable work on plants and animals 

 has demonstrated that the somatic number is the same as the 

 diploid number of the germ cells. To mention but a few — the 

 studies on the squash bug (^lorril, '13), Hoy ('16), those on 

 many of the Oenotheras (Gates '15), the work on the mosquito 

 and the Drosophila (Metz, '14 and '16, WTiiting, '17 and Hance, 

 '17) have all irrefutably shown that the two types of cells are 

 alike in chromosome numbers. 



What, then, does the fact mean that, on the one hand, we find 

 the somatic chromosomes breaking up, while, on the other, they 

 are constant in form and number? In the case of Oenothera 

 scintillans I have pointed out that this is the most unstable of 

 all the 'mutants' of the Oenothera series and never breeds true. 



