46 John Henry Comstock 



specialization may undergo marked changes in the course of 

 the history of a single line of development. Thus I feel sure 

 that iu the ancient Frenat^e the tendency of specialization 

 was towards more rapid flight which tendency resulted in the 

 preservation of the narrower winged forms. But while this 

 tendency has been continued in certain divi-sions of the group 

 to the present time, so that in these divisions the most highly 

 specialized forms have the narrowest wings (Sphingidae, 

 Zygsenina), there are other divisions in which the tendency 

 has been changed towards a different mode of flight, and has 

 resulted in the preservation of the wider winged forms, and in 

 these divisions the most highly specialized forms are those 

 having the widest wings, (Saturniina.) 



In recording the results of specialization one is apt to speak 

 as if there were an intelligent directing force which determines 

 the direction of specialization ; or as if individuals deliber- 

 ately chose the way in which they should vary from their pro- 

 genitors. The fact that we are often able to arrange the mem- 

 bers of a group in well defined series, each series culminating 

 in a specialized form towards which the other forms approxi- 

 mate in varying degrees of closeness, leads to the unconscious 

 use of such expressions. It is difficult to keep constantly in 

 mind the extent of the thinning out process that takes place 

 in nature, that the objects of our studies are merely a few for- 

 tunate individuals that have withstood tests that have proved 

 fatal to the great majority. Innumerable unfortunate varia- 

 tions perish and leave no record ; we see the fortunate ones 

 alone ; and the impression is apt to be that there is a definite 

 progression on the part of all. Perhaps the facts of the case 

 can be expressed as follows : The conditions which surround 

 an organism combined with the existing structure of that 

 organism render variations in its offspring in certain definite 

 directions fortunate, while variations in other directions are 

 unfortunate. As the fortunate variations alone are preserved 

 to us the record seems to indicate a strong tendency to vary in 

 definite directions. 



In this paper the terms generalized and specialized are used 

 in preference to low and high, which are often loosely used as 



