i8g 4 .] 



THE BRITISH NATURALIST. 



53 



organ, to the wing, a locomotory organ, was effected; it is scarcely 

 necessary here to say that structurally an insect's wing resembles the 

 gill-leaflet of an ephemerid larva. Since no individual of any of the other 

 five classes of air-breathing Arthropods has any trace of wings, we may 

 certainly say that there has been no reversion to an aquatic life amongst 

 their ancestors since they emerged from the worm type and reached the 

 peripatus level. 



The power of flight which the large majority of insects possess has 

 doubtless been the cause of their success in the struggle for existence, 

 and has led to the enormous multiplication of their species, and individuals. 

 Every insect has six legs, and (save a few apterous forms) one or two 

 pairs of wings. 



The class Insecta is divided into many orders, some entomologists 

 making 16, but I prefer to restrict the number to 8, viz., Orthoptera, 

 Neuroptera, Trichoptera, Hymenoptera, Coleoptera, Hemiptera, Lepi- 

 doptera, and Diptera. The first five have mandibulate or biting mouths, 

 the last three haustellate or sucking mouths. Although there is great 

 difference between the two kinds of mouths, yet a close examination shows 

 that both are but modifications of the same parts. They are six, the 

 labrum or upper lip, which is a median plate formed from the lower 

 portion of the head. There are two mandibles, two maxillae, and a 

 second pair of maxillae, which form the labium. Wherever we find 

 appendages to the mouth they are situated on the lower parts, viz., the 

 maxillae or labium. 



Wonderful as these modifications are, yet we can trace the develop- 

 ment of them all from ambulatory legs. It may seem incredible, but it is 

 nevertheless true, and the transition may be indicated by pointing out 

 that the proboscis of a butterfly is developed from the maxillae of the 

 caterpillar, the rostrum or beak of the bug from the labium of the 

 biting insect ; the tongue of the bee from the lining of the inside of the 

 labium, whilst the simpler forms of labia plainly show relationship to the 

 second pair of maxillae in those myriapods whose homologues in the 

 still simpler Peripatus are locomotory organs. 



Of the real relationship of the 278 thousand species of air-breathing 

 Arthropods I have not the least doubt ; whether I have succeeded in 

 making it clear to my readers remains to be seen. It has not been my 

 object to show the connection between the orders which make up the 

 great classes, but between the classes themselves. The evidence 

 adduced may by some be regarded as indecisive, but if the homologies 

 be real, the inferences can scarcely be inaccurate. So far as I know, 

 all the facts, anatomical, embryological, and palaeontological, are in 

 complete accord with' the theory I have laid before you. This being the 

 case, it may be provisionally accepted as a working hypothesis, with a 

 strong balance of probability in its favour. Anyone who has gone 



