2 



INTRODUCTION. 



of natural selection, combined probably with disuse. For during 

 many successive generations each individual beetle which flew 

 least, either from its wings having been ever so little less perfectly 

 developed, or from indolent habit, will have had the best chance of 

 surviving from not being blown out to sea ; and, on the other hand, 

 those beetles which most readily took to flight would oftenest have 

 been blown to sea, and thus destroyed."* 



Whether Darwin's inferences are correct may be doubted, for 

 large and powerful forms with rudimentary wings occur far from 

 the sea, but the facts with regard to Madeira are certainly 

 striking. 



In some forms of Coleoptera the elytra are not evenly joined at 

 the suture, and in some (e. g. Sitaris, Meloe, etc.) there is no 

 suture at all, the elytra being quite separated or to a greater or 

 lesser extent overlapping. 



The venation of the elytra is, as a rule, not evident, as might be 

 expected from the material of which they are composed, but the 

 venation of the wings is very distinct and varies very considerably. 

 Until quite recently very little use has been made of this character 

 in the Coleoptera, although the importance of the neuration of the 

 wings has long been recognized in the Lepidoptera and, to a less 

 extent, in tiie Diptera ; much more attention is now being paid 

 to it as an aid to classification, and it will be referred to at greater 

 length further on. 



External Structure. 



The principal parts of the body are the head, tJiora.r, and 

 abdomen. The head is free and very mobile, usually short and 

 normal, but occasionally more or less produced, and in most of the 

 Kiiynchophora provided with a rostrum or beak-like process : this 

 rostrum is in no sense a trunk, but an integral part of the head, and 

 the mouth organs are situated not at its base, as might be supposed, 

 but at its apex : the front of the head is often called the vertex and 

 the hinder part the occiput, but as the occiput proper is not found 

 in the Coleoptera, the upper surface of the head as visible is 

 commonly spoken of as the vertex : in front of the vertex and 

 usually separated from it by a distinct suture lies the clypeus or 

 eplstoma. 



The mouth organs proper consist of a labrum or upper lip, which 

 adjoins the clypeus and is sometimes hidden behind it, or even 

 connate with it ; it is very variable in size, and is absent in the 

 Khynchophora except in the EhinomaceridoE, Antiiribidje, and 

 Platypid^e. In some orders of insects {e. g. Neuroptera) the 

 clypeus is often divided into two parts, while in others (e. c/. 

 Siphonaptera) both the clypeus and labrum are wanting. Beneath 

 the labrum come the large jaws or mandibles ; these vary according 

 to the food of the insect. In the carnivorous beetles they are 



* Origin of Species, Oth Ed. p. 109. 



