k; 



PSYCHE. 



[February iSg/. 



from each other. But, after all, both 

 larva and imago live on vegetable food, 

 and more than this, in the higher mem- 

 bers of the group at least, on very nearly 

 the same kind of vegetable food, the 

 leaves and flowers of phanerogamous 

 plants. The larva eats and lives among 

 the green leaves, while the imago finds 

 its nourishment in the flowers which are 

 modified leaves. So that we shall not 

 be surprised if we find that the transfor- 

 mations which result in the producl:ion 

 of the butterfly from the caterpillar are 

 not as great as the apparently great dif- 

 ference between the two forms might 

 suggest. As is the case with the 

 coleoptera, the imago acquires wings, 

 compound eyes, and external reproduc- 

 tive organs, and all the larval organs 

 with the exception of the midgut pass 

 directlv into the imaginal organs, al- 

 though some of them are highly modi- 

 fied in the process ; but there is no 

 complete making over, no general his- 

 tolysis. 



In the hymenoptera the larva and 

 imago live in general on the same kind 

 of food. But the conditions of colon- 

 ial and family life which prevail among 

 the higher members of the order have 

 resulted in a maiked retrogressive de- 

 velopment on the part of the larva, so 

 that it is very diflerent structurally, from 

 the imago. Not having to find its own 

 food, to protect itself, or to escape from 

 enemies, it has lost its extremities. In 

 the nematoceran diptera other conditions 

 have produced similar results, and we 

 also find apodous larvae. The transfor- 

 mations, now. which the pupae of tliese 



insects must undergo to become imagin- 

 es are much greater than is the case in 

 the coleoptera or lepidoptera. Not only 

 must wings be acqiured during the 

 metamorphosis but legs as well, and the 

 larval organs require a much greater 

 modification before they can serve as 

 imaginal organs. But yet no complete 

 making over, no general histolysis * 

 takes place. 



When we come to the brachyceran 

 diptera, the most highly specialized in- 

 sects in m}' opinion, we find the great- 

 est structural differences between the 

 larva and the imago to be met among 

 insects. The environment of the larva 

 is as a rule totally different from that of 

 the imago, and the larval structure 

 corresponding!}- different from the imag- 

 inal. The larva, too, has undergone an 

 extensive retrogressive development. 

 In the case of the nematocera, as I have 

 just said, the larva is without legs, but 

 \\\ the brachycera the retrogression has 

 gone much further and the larva has 

 neither legs nor head. There are also 

 great internal differences. In the meta- 

 morphosis, consequently, a very differ- 

 ent animal must come out of the pupa- 

 rium than went into it. The imago 

 must acquire not only external repro- 

 ductive organs, compound eyes, wings, 

 legs, and a head, none of which the 

 larva possessed, but also internal organs 

 very different from those of the larva. 

 A complete making over accompanied 

 bv general histolysis is the result. 



* Ganiu, M. The post embr>'onic development of insects. 

 /Russian ) Warsaw 1S76. Renewed in Zeit. f. Wiss. Zool. 

 2SBd. 1S77; P- 3^6- 



