334 c - E - MCCLUNG. 



are produced four sorts of spermatozoa with regard to the com- 

 binations of chromosomes, but two kinds with respect to the 

 presence or absence of certain ones of a multiple. In order that 

 always the same combination of chromosomes (so far as size is 

 concerned, and this appears necessary to satisfy the observations) 

 should appear in the spermatocytes, it would be necessary for 

 eggs with the missing elements to be present and to be fertilized 

 with the proper spermatozoa. The exact nature of this coordi- 

 nate action cannot now be determined for we are lacking sufficient 

 data, but that it must exist seems apparent from the observation 

 that always the same sized complex reappears in each generation 

 of first spermatocytes. From even our limited knowledge it 

 seems evident that there is great precision and definiteness of 

 organization necessary to bring about in successive generations 

 of similar cells the same grouping of chromosomes. That the 

 entire cell is involved in this organization is, I think, indicated by 

 my observations on the spermatocytes of filcnniria where it ap- 

 pears that practically the whole of the cell material is bipolarized 

 and thus accurately divided by mitosis. 



The fact that there exists an orderly sequence of concerted 

 movements on the part of the chromosomes suggests many inter- 

 esting possibilities and offers opportunities for many speculations 

 and theories, but it would seem wise to await the determination 

 of more facts and a careful cooperative study of the species in- 

 volved before venturing into speculation. Because of the impor- 

 tance attaching to these observations it has seemed desirable to 

 make them known now in the hope that similar phenomena may 

 be observed in other objects. Every additional fact of this sort 

 largely increases the prospect of our attaining an understanding 

 of the mechanism of the hereditary transmission of characters, 

 and if it can be found that a peculiar association of chromosomes 

 is always accompanied by a characteristic arrangement of the 

 body parts then we may begin to see the relation between germ 

 cell architecture and somatic structure. 



Among the uncertainties in my mind concerning the behavior 

 of the chromosomes in Mermiria is one relating to the nature of 

 the association of the chromosomes into the multiple element of 

 the first spermatocyte. The tetrads seem of the usual type, /. e., 



