INSECTS IN GENERAL. 3 



tailed insects (as an order named Tliysanura from Latreille), 

 and the lice (as an order named Anoplura or the Parasita Latr.) were 

 united with insects as a subclass under the name of Ametabolia.* 

 Mr. Curtis has adopted the group of insects as thus extended by Dr. 

 Leach. By Latreille the spring-tailed insects and -HMtes have been 

 constantly regarded as belonging to the class of insects, from their 

 possessing six legs, in common with the metamorphotic insects ; and 

 the mites have been constantly regarded as portion of the class 

 Arachnida, from possessing in common with the spiders eight legs. 

 The Centipedes, however, have been variously regarded by Latreille, 

 either as forming a distinct order of insects, under the name of 

 Myriapoda (as in the 2d edition of the Regne Atiimaf), or as con- 

 stituting of themselves a distinct fourth Annulose class (as in his last 

 work, Cours d' Entomologie, 1831.) 



Messrs. Kirby and Spence have adopted a classification totally dif- 

 ferent from that of all preceding or subsequent systematists, in which 

 three Annulose classes are formed, namely, Crustacea, Arachnida, 

 and Insecta; but the latter is augmented by the hexapod spring- 

 tailed insects and lice, the octopod mites, and the polypod centipedes, 

 all of which are regarded as forming a single order, Aptera, charac- 

 terised by respiring by tracheae, and having no system of circulation. 

 [Introd. iii. p. 22.) The incongruous character of the groups thus 

 associated together ; the possession of pulmonary sacs by Thelypho- 

 nus, which is thus placed amongst the mites ; the recent researches 

 of M. Duges on the respiratory organs of Dysdera and Segestria, 

 read before the Academic des Sciences on the 9th February, 1835, 

 (clearly demonstrating that the respiratory system in the Arachnida 

 is not entitled to pre-eminence as a character of the class) ; and, 

 lastly, the admission of Messrs. Kirby and Spence themselves (^Introd. 

 iv. 383.), that their order Aptera is not a natural, but merely a pro- 

 visional one, and that the hexapod insects are to be regarded as more 

 peculiarly entitled to the denomination of Insects {Introd. iii. 22.), 

 will, I trust, be considered as sufficient to authorise me in not adopt- 

 ing their views. 



Mr. Stephens, in addition to the ordinary metamorphotic groups, 

 has added the lice (Anoplura) to the class of insects, without, how- 

 ever, offering an argument for this deviation from all previous systems. 

 The general construction of the hexapod antenniferous body of the 



* Edinb. Encycl. vol, ix, 

 B 2 



