326 C. E. MCCLUNG. 



individual chromosome and certain characters of the body. Un- 

 fortunately we have no answers for these questions and they 

 become, in fact, a part of the general problem. 



As has been stated, the ultimate aim of these studies is to 

 determine the relation between individual chromosomes and char- 

 acters in the body, but this specific knowledge will come last of 

 all and only after the most extensive investigations, so it is need- 

 less to say that as yet nothing has been discovered concerning 

 the suspected relationship. What will first be accomplished will 

 be the determination of the nature and behavior of the chromo- 

 somes in different species and from these observations some sug- 

 gestions regarding the mechanism of the chromatin elements in 

 heredity may be advanced. This knowledge may come about 

 by a comparison of the germ cells and body characters in nearly 

 related species, by observing the differences in germ cells of indi- 

 viduals that vary from the type of the species, or finally by 

 experimentally disturbing the normal conditions in the germ cells 

 and observing the effects upon the body. An attack on the 

 problem must begin, then, by a search for differences between the 

 germ cells of related species and between those of related genera, 

 and in the present instance concerns certain forms that show 

 very striking arrangements of the elements. 



Upon the theory of the primary importance of the chromo- 

 somes in heredity we are forced to assume that the development 

 of the characters in the individual of the genus Hesperoteltix is 

 the result of a definite composition and arrangement of the chro- 

 matic elements in the germ cells. Since definiteness of number, 

 composition, and arrangement of the chromosomes always pre- 

 cedes the exhibition of a certain series of characters in the 

 organism, it must be true that an alteration in either the number, 

 composition, or arrangement of the chromosomes would be fol- 

 lowed by the development of a somewhat different series of body 

 characters. As I have previously mentioned, the number of 

 chromosomes does not vary, nor is it possible to detect any dif- 

 ference in the composition of the chromosomes (although of 

 course it occurs), but a characteristic arrangement of the chromo- 

 somes distinguishes this genus from others in the family, and so 

 we must conclude that this is genetically connected with the 

 subsequently appearing characters. 



