265 



[Packard. 



psedia Biitannica, " Otliedit., Mr. R. McLachlan claimed that these insects 

 should be regarded as degraded Pseudoneuroptera. This view seems a 

 natural one. Struck by this suggestion, and before reading Nitzsch's 

 essay on the internal anatomy of Atropos, we had been led into compari- 

 sons with the Psocida?, particularly the wingless form Atropos, to which, 

 as we hope to show, with the aid of Grosse's results, the bird-lice are 

 more closely allied than to any other group of insects. Grosse himself, 

 unfortunately does not intimate what his views are as to the exact sys- 

 tematic position of the group under consideration, beyond affirming that 

 they certainly are not Hemiptera. 



We will now turn to the conclusions of jNIelnikow,* derived from a study 

 of the embryology both of the Mallophaga and the true lice. In this 

 essay the author thus sums up his views as to the affinities of the Mallo- 

 phaga : 



"The study of the embryology of the Pediculida? and Mallophaga 

 affords proof of a complete similarity in the mode of development of these 

 two groups of animals. We are convinced that the similarity urged is 

 seen not only in the identity of the formation of the primitive streak and 

 the relations of the embryonal membranes, but also in other more subor- 

 dinate features of the development. We have for example perceived that 

 in the lice as well as the Mallophaga a provisional mass of cells is formed 

 before the completion of the blastoderm ; that both have the provisional 

 membrane which the larva leaves behind it in the egg at the time of 

 hatching. Finally we are in a position to state that the beaks of both 

 groups of insects are independently formed of the appendages of the head- 

 segments. 



"These, though subordinate processes of development, appear to us to 

 be of more value in the comparison of the insects under consideration than 

 the relations of the mode of formation of the primitive streak and of the 

 embryonal membranes, since the last without doubt is generally common 

 to those insects with an internal primitive streak, but the former must be 

 regarded as the distinctive feature of the insects under consideration. 



"If we add to the results mentioned, the fact that the anatomical struc- 

 ture of the mouth-parts in the insects of the two groups agrees in all 

 essential points ; if we add the generally similar external form of these 

 insects, finally their ectoparasitic mode of life, then we need not hesitate 

 to recognize the close relationship of the lice and Mallophaga. 



"This conviction is not insignificant, since it aftbrds us the possibility 

 of decisively answering the question as to the systematic position of these 

 insects. 



"After the researches of Burmeister it was generally considered that 

 the Pediculidaj belonged to the Hemiptera. The structure of their mouth- 

 parts and the incomplete metamorphosis they undergo are the reasons 

 which confirm such a view. 



* Beitriige zur embryonal Entwickelung der Insektcn. Archiv f. Natur-Gesch., xxxv 

 1869. 



PUOC. AMER. PHILOS. SOC. XXIY. 126. 2h. PUtNTED NOV. 2, 1887. 



