156 PROC. ENT. SOC. WASH., VOL. 24, NO. 6, JUNE, 1922 



The evidence of the head capsule is thus seen to be in complete 

 agreement with that drawn from other structures of the body, 

 which in every case points very clearly to the Crustacea as the 

 nearest known representatives of the types ancestral to insects; 

 and, while the isopods themselves are not to be regarded as 

 representing the actual ancestors of any insects, they, together 

 with the insects and myriopods, were apparently descended 

 from common ancestors related to the Mysidacea, Anaspidacea, 

 and similar crustacean forms. As the three lines of descent 

 emerged from this common ancestry, the line of descent of the 

 "myriopods" paralleled that of insects for a short distance on 

 the one side, while the line of descent of the isopods and higher 

 Crustacea paralleled that of the insects on the other side for a 

 much longer time (or greater distance) than is true of the 

 myriopodan line of development. This dual relationship of 

 insects to the higher Crustacea and to the "Myriopoda, " 

 however, has been fully discussed elsewhere (see Fiftieth Rpt. 

 Ent. Soc. Ontario for 1919, etc.) and need not be further 

 discussed here. 



In the 1921 volume of the Transactions of the Entomological 

 Society of London (p. 340) attention was called to the fact that 

 the head of a higher crustacean is composed of one more seg- 

 ment than the head capsule of an insect, since in the higher 

 Crustacea, the first maxilliped becomes closely associated with 

 the head capsule and even in chilopods, the "poison claws," 

 which are homologous with the first maxillipeds of Crustacea, 

 tend to become more closely associated with the head than 

 with the trunk region. In the article in question, the parag- 

 naths (also called superlinguae, 1 "maxillulae," or "paraglossae") 

 were attributed to the first maxillary segment of the head in 

 insects, Crustacea, etc., but, as I have pointed out in a subse- 

 quent paper published in these Proceedings, the embryological 

 evidence points to a mandibular origin of the "superlinguae" 

 (paragnaths) in insects and higher Crustacea, so that the ap- 

 pended table, in which the segments of the head are compared in 

 insects, chilopods, and crustaceans, is more nearly in accord 

 with the embryological evidence of the nature of the compo- 

 sition of the head, than is the case with the table given in the 

 former article. 



1 Dr. Folsom developed purely as a side issue of his classic monograph on the 

 development of the head structures of Anurida, the view that the superlinguae 

 '(paragnaths) of insects represent the maxillulae of Crustacea, and in attacking 

 the tenability of this view, I would most vigorously disclaim any intentions 

 whatsoever of calling into question the correctness of the main features of Dr. 

 Folsom's investigations, which were admirably executed, and were carried out 

 .in an exceptionally thorough manner. 



