86 THE ENTOMOLOGIST. 



these curious modifications. He treats as quite open to dis- 

 cussion the view that these are the original forms oilepidopterous 

 trojjhi, and that the ordinary forms are a further development, 

 but decides against it. I think we may follow him here without 

 the least hesitation. This group is a solitary one. There is no 

 other group showing such modified structures, and it is a very 

 long way indeed from being one of the lowest groups. So that 

 it is improbable in the last degree that a primary condition like 

 this is, if it be one, should be preserved here, and here only. 

 This, when we consider only the Lepidoptera ; but we have to 

 remember that the ordinary form of lepidopterous tropin falls 

 into line with that in other insects, whilst that of the early 

 Gracilariad larva does not. 



We are forced, I think, to conclude that this special form of 

 larva is derived from the ordinary form by selective modification. 

 Mr. Chambers speaks of these changes as degradation and 

 elevation. There is a certain convenience in so doing. 

 The absolute loss of labial and maxillary palpi, just like the loss 

 of true legs and of prolegs, which occurs in so many other larvae 

 as well as these, may be spoken of as degradation. But the 

 marvellous modification of the jaws and of the labrum and 

 labium to enable a very special form of feeding to be carried 

 out is rather elevation than otherwise. They are at least 

 evolutionary changes. Whether we call them degradations or 

 elevation is rather a matter of the personal equation of the 

 observer than of the facts themselves. No doubt we incline to 

 say that an organ that becomes more complicated is advancing, 

 one that is simplified is degrading ; and probably this is correct 

 if we apply it to the organ considered, and not to the whole 

 organism. With regard to our larva, it is specialized, therefore 

 elevated ; the jaws and labium and labrum are specialized, 

 therefore an advance; the loss of palpi, &c., is a degradation; 

 but the whole insect is advanced. In modification of any 

 question of advance or retreat, we must remember that the lost 

 processes, palpi, feet, &c., are merely in abeyance, not lost; 

 their embryonic nuclei persist and give rise to them in the later 

 stages. 



The great interest from an evolutionary point of view of 

 these larvse is from a rather different aspect. Our ordinary 

 view of larval evolution in the Lepidoptera is that during the 

 whole of larval life selection is acting on the larva, and produces 

 its greatest effect on the full-grown larva, and that the characters 

 so acquired by the adult larva tend to pass backwards to earlier 

 moults, so that a primitive condition may persist up to the last 

 moult, or may be lost earlier, and we find as a very common 

 occurrence some primitive condition present in the first instar, 

 but not afterwards. And, finally, the backward pressure of 

 evolutionary changes annexes the first instar also, and that 



