ANURIDA. 355 



It has been necessary to consult a considerable 

 amount of literature while preparing this Memoir, and I 

 wish to acknowledge my indebtedness more particularly 

 to the writings of Fernald, Folsoni and Will em. They are 

 numbered 8, 10 and 27 respectively in the bibliography 

 to be found at the end. 



I. INTRODUCTORY REMARKS. 



The general characters of the class Insecta are familiar 

 to every student of Zoology. Among this vast assemblage 

 of animal forms, there is an obscure group of great 

 phylogenetic importance possessing certain definite 

 characters which separate it from the other members of 

 that class. Until comparatively recently, it has been 

 customary to regard this group as constituting a single 

 order, viz., the Aptera, and the latter was divided into the 

 two sub-orders Collembola and Thysanura. It was in the 

 year 1885 that Brauer recognised that the Aptera 

 possessed characters which merited their being raised to 

 something more than ordinal rank. He, therefore, 

 proposed to call them Apterygogenea in contradistinction 

 from the rest of the Insecta, which he termed 

 Pterygogenea. The investigations of the last thirteen 

 years all tend to establish Brauer' s contention. In 

 preference, however, to his terms, the shortened names of 

 Apterygota and Pterygota are in more general use. 



The following characters, taken collectively, 

 separate the Apterygota from the rest of the Insecta or 

 Pterygota : — 



(1) The absence of any true process of metamorphosis. 



(2) The total absence of wings. 



(3) The presence of an evident pair of mouth-parts, 



the maxillulye, intercalated between the 

 mandibles and first maxillae. 



