42 ON PLANTS AND INSECTS. [LECT. 



to the mature form ; and adaptation al or adaptive ; those 

 which tend to suit them to their own mode of life. 



It is a remarkable fact, that the forms of larvae do not 

 depend on that of the mature insect. In many cases, for 

 instance, very similar larvae produce extremely dissimilar 

 insects. In other cases, similar, or comparatively similar, 

 perfect insects have very dissimilar larvae. Indeed, a 

 classification of insects founded on larvae would be 

 quite different from that founded on the perfect insects. 

 The Hymenoptera, for instance, which so far as the 

 perfect insects are concerned, form a very homogeneous 

 group, would be divided into two or rather one portion 

 of them, namely, the saw-flies, would be united to th e 

 butterflies and moths. Now, why do the larvae of saw- 

 flies differ from those of other Hymenoptera, and 

 resemble those of butterflies and moths ? It is because 

 their habits differ from those of other Hymenoptera, 

 and they feed on leaves, like ordinary caterpillars. 



In some cases the form changes considerably during 

 the larval state. From this point of view, the trans- 

 formations of the genus Sitaris, which has been carefully 

 investigated by M. Fabre, are peculiarly interesting. 



The genus Sitaris (a small beetle allied to Cantharis, 

 the blister-fly, and to the oil-beetle) is parasitic on a 

 kind of bee (Antliophora) which excavates subterranean 

 galleries, each leading to a cell. The eggs of the sitaris, 

 which are deposited at the entrance of the galleries, are 

 hatched at the end of September or beginning of Octo- 

 ber, and M. Fabre not unnaturally expected tha't the 

 young larvae, which are active little creatures with six 

 serviceable legs, would at once eat their way into the 

 cells of the anthophora. No such thing : till the month 



