Collembola and Thysanura 34; 



gogenea on account of the belief that absence of 

 wings among them is a primitive character, and not 

 the result of degradation. No species of either order 

 is known to possess the vestige of a wing. While 

 giving due weight to this evidence it may be doubted 

 whether primitive winglessness, even if admitted, can 

 be looked upon as a primary dividing character among 

 insects. The Collembola, at any rate, cannot be re- 

 garded as a primitive group. The in-pushing of the 

 head-skeleton so that the jaws appear to be inside it, 

 and the reduction of the abdominal segments to five 

 or six, show very decided specialisation, as do the 

 presence of the spring — a most curious organ un- 

 known in any other group of insects — and the post- 

 antennal sense-organ, also peculiar to the order. 

 Moreover, the families of Collembola are fairly rich 

 in genera and species, mostly with a very wide and 

 continuous range. On the whole the Collembola 

 must be regarded as a group of insects, in some 

 respects specialised, in others degraded, in corres- 

 pondence with their life in concealed and under- 

 ground situations. And it must be remembered 

 that life in such situations would certainly tend to 

 the total loss of wings. 



The Thysanura, on the other hand, have more 

 claim to be considered primitive. They have the 

 full number of abdominal segments, many of which 

 bear short limbs, while the jaws in the less degraded 

 forms are similar to those of the normal biting insect. 

 Moreover, they are clearly a decadent group, each 

 family containing as a rule but one or two genera. 

 Taking all the facts into consideration the Thysanura 

 must undoubtedly be regarded as the lowest of living 

 insects. And it is interesting to notice that in those 

 genera — Campodea and lapyx — which live in the 

 most obscure situations, such apparent retraction of 



