92 ON THE ORIGIN AND [CHAP. 



occurs in many orders of insects. It is true that the 

 mouth-parts of Campodea do not resemble either 

 the strongly mandibulate form which prevails among 

 the larvae of Coleoptera, Orthoptera, Neuroptera, 

 Hymenoptera, Lepidoptera ; or the suctorial type of 

 the Homoptera and Heteroptera. It is, however, not 

 the less interesting or significant on that account, 

 since, as I have elsewhere l pointed out, its mouth- 

 parts are intermediate between the mandibulate 

 and haustellate types ; a fact which seems to me 

 most suggestive. 



It appears, then, that there are good grounds for 

 considering that the various types of insects are 

 descended from ancestors more or less resembling 

 the genus Campodea, with a body divided into head, 

 thorax, and abdomen : the head provided with 

 mouth-parts, eyes, and one pair of antennae ; the 

 thorax with three pairs of legs ; and the abdomen, in 

 all probability, with caudal appendages. 



If these views are correct, the genus Campodea 

 must be regarded as a form of remarkable interest 

 since it is the living representative of a primaeval 

 type, from which not only the Collembola and Thy- 

 sanura, but the other great orders of insects have 

 derived their origin. 



From what lower group the Campodea type was 

 itself derived is a question of great difficulty. Fritz 

 Miiller indeed says, 2 " if all the classes of Arthropoda 

 (Crustacea, Insecta, Myriopoda, and Arachnida) are 

 indeed all branches of a common stem (and of this 

 there can scarcely be a doubt), it is evident that 



1 Linnean Journal, vol. xi. 2 Facts for Darwin, p. 120. 



