88 THE ENTOMOLOGIST. 



changes in full-grown larvae gradually pushing their way back to 

 the earlier instars. What we learn here, however, is that each 

 larval instar is a stage, comparable to the pupal or imaginal 

 stage in its individual importance, and that it may undergo 

 changes without necessarily involving any other instar, which 

 holds to it the attitude of a separate stage. 



In the larval state there are no doubt two conditions at work; 

 the one is the tendency of a peculiarity acquired at any stage to 

 be passed to the preceding and following stages — a tendency 

 that will gradually produce an effect on these adjacent stages 

 unless they resist it. This they will do should the peculiarity 

 be such as to produce harmful effects if passed on to them. The 

 other condition is that the full-grown larva has usually to adapt 

 itself to conditions that are much more various than those 

 affecting the young larva, and so the adult larva is much more 

 liable to varied specialization than it is in its earlier instars. 



Essentially, nevertheless, the young larva is just as liable to 

 specialize in view of changed conditions as the adult one is. 



This consideration, if we could always keep it in view, 

 especially if we could recognize and understand the cases in 

 which it occurs, would often assist us very much in overcoming 

 difficulties that arise from supposing that young larvae are 

 always less modified than older ones ; and especially that such 

 modifications as they present are reminiscences of modifications 

 acquired by the adult larvae of some or other of their ancestors. 



As a possible instance, I may remind you of the young larva 

 of Pajnlio machaon. This larva seems obviously reminiscent of 

 an adult Vanessa larva. Yet it is certain that, whether Vanessa 

 be or be not derived from a Papilio-\\\ie form, Papilio is certainly 

 not derived from any Nymphalid, nor is there any probability 

 that any adult Papilio larva ever was spinous in precisely this 

 manner. 



The spines are a special development of the young Papilio 

 larva for protective objects affecting itself. They have not been 

 derived from spinous full-grown larvae amongst their ancestors, 

 and are not passed on to the present adult larva because it does 

 not require them. 



The processes on adult larvae of Ornithoptera and of Clytia 

 are not spinous, so as to be ancestral to those of young Machaon, 

 but may themselves be derived from the spines of the first 

 stage. 



As I have said, however, this and other instances are open 

 to some doubt, and the case of Gracilaria, in which doubt is 

 difficult to insinuate, is useful, as giving us a standpoint different 

 from that usually held. 



(To be continued.) 



