EXPERIMENTS IN THE BREEDING OF CERIONS. 49 



Cerion incanum (Binney) X Cerion viaregis Bartsch. 



I am sure that all naturalists who have prepared monographs upon 

 large groups of animals have at times been puzzled how to treat 

 systematically and how to account for some of the remarkably variable 

 species which one occasionally finds. It usually happens that in a large 

 genus almost all the forms are clearly defined and easily recognized 

 specifically and there is never a question as to which species a given 

 individual belongs. Now and then, however, one finds a group the 

 members of which are readily recognized as closely related through some 

 characteristic feature in spite of the fact that scarcely two individuals 

 appear to be alike and that some of the extremes of these variants, 

 were their character fixed, would demand a place in a different subgenus 

 from that to which the norm of the group belongs (e. g., Odostomia 

 {Evalea) virginalis Carpenter, from the West Coast of America). 

 Usually this state of affairs is accompanied by the production of a large 

 number of individuals; in fact, these variable forms are usually the 

 dominant element in the region. Not only that, but as a rule we find 

 that such forms are not confined to one faunal area, but appear to be 

 able to extend their range over one or more of the adjacent areas. 

 Organisms presenting such conditions have been said to be in a state of 

 flux. It has been held by some that this variabiUty is an expression of 

 an effort on the part of a species to adjust itself to changing or changed 

 environmental conditions, which, for the time being, affect it adversely. 

 The followers of this hypothesis conceive that the organism, adversely 

 struggling, is putting out an endless array of feelers in the hope of finding 

 a better way or better ways for continued existence. This hypothesis, 

 while it may be true in some cases, does not seem to obtain in the varia- 

 ble forms which have come under my observation, for it scarcely seems 

 possible that the numerically and apparently physically dominant and 

 most widely distributed form of a group in a certain region should be the 

 one least suited to the environment in which it is existing. Prior to 

 this year I was more and more inclined to the belief that we might 

 possibly find that these very abundant and variable forms might repre- 

 sent new ingressions into a faunal area in which conditions for their 

 existence were optimum to an unusual degree, where the normal death 

 rate, due possibly to an absence of natural enemies, might be reduced, 

 and where all the factors involved were inclined to favor the new arrival 

 to the utmost, and that these factors and the necessarily reduced 

 in-breeding might be responsible for the loosening of specific bounds 

 and the producing of variants which, in the course of time, might 

 result in a state of flux. 



Our Cerion experiments on Newfound Harbor Key, however, throw 

 a new light upon the case, for here we have produced a state of flux by 

 cross-breeding. There is no question that if we did not know the true 

 inwardness of the Cerion complex as it exists at the present time in our 



