344 Annals Entomological Society of America [Vol. X, 



terminal abdominal structures, etc., a comparative study of 

 the head capsule in the insects in question would indicate 

 that the line of development of the Trichoptera branched off 

 from the common ancestral " Neuropteroid " stem at a point 

 not far distant from the origin of the Mecopteron line of develop- 

 ment. The ultimate ancestors of the Diptera were Neuropteron- 

 like (the tendency toward the reduction of the hind wings 

 occurring regularly in such Neuroptera as Nemoptera, and 

 occasionally in such forms as Psectra, etc.) and they were related 

 to . both the ancestral Trichoptera and Mecoptera. The 

 Dipteron line of development, however, has paralleled that of 

 the Mecoptera remarkably closely (more so in fact than any 

 other insects) and since the Mecoptera have "lagged behind," 

 or have not travelled as far along the road to specialization as 

 the Diptera have, they have remained in many respects strik- 

 ingly like the ancestors of the Diptera, so that a study of their 

 structures will frequently serve to indicate the steps by means 

 of which the more highly modified homologous structures in 

 the Diptera have reached their present state, in following out 

 certain evolutionary tendencies present in both lines of develop- 

 ment. 



BIBLIOGRAPHY. 

 1895. Felt— The Scorpion Flies: Report State Entomologist, N. Y., 10, 1895, p.463. 

 1913. Miyake- — Studies on the Mecoptera of Japan: Jour. Coll. Agr. Imp. Univ. 



Tokyo, 6, No. 6, p. 265. 

 1916. Peterson — The Head Capsule and Mouthparts of Diptera: 111. Biol. 



Monographs, Vol. 3, No. 2, p. 1. 



A more complete list of the articles dealing with the mouth- 

 parts and phylogeny of the insects under consideration will 

 be given in articles dealing with these phases of the subject. 



