Insect-Orders 345 



which show generalised structure are believed to 

 be more ancient than those which exhibit great 

 specialisation. And the life-history of the individual 

 is believed to indicate to some extent the life of the 

 race. For example an insect like a Termite with 

 four similar wings is considered lower or more 

 primitive than one like a House-fly in which the 

 hind-wings are represented by stalked knobs. And 

 the fact that rudiments of limbs appear on the 

 abdominal segments of many insect embryos is 

 thought to indicate that the remote ancestors of 

 insects had legs on the hind-body as well as on 

 the thorax. But these two principles must be 

 used with the greatest care, and especially in the 

 study of insects. So many insects are clearly 

 degenerate that the naturalist must always consider 

 the possibility of generalised structure pointing to 

 degradation rather than to antiquity. And the 

 striking changes which many insects pass thi-ough 

 after hatching greatly complicate the task of inter- 

 preting their life-histories. 



Reference has already been made (Chapter IV, 

 p. 164) to the various lai-ge divisions into which it 

 has been proposed to group the insect orders. The 

 Mandibulata, or insects with biting jaws, are, on the 

 whole, lower than the Haustellata or insects with jaws 

 adapted for piercing or sucking, since in the latter 

 the individual jaws are so highly modified that their 

 typical parts can be recognised only with great diffi- 

 culty or not at all. A Moth is distinctly a higher insect 

 than a Cockroach. But is it possible absolutely to 

 settle the position of insects by this test ? Is a Beetle, 

 for instance, a lower insect than a Bug? Turning 

 to the other chief division of the insect-orders which 

 has been proposed — that which depends on the 

 life-history — we remember that the bug comes into 



