Phylctic Parallelism in Metamorphie Sfxcies. 429 



varieties of the fourth stage sometimes become 

 the lightest forms of the fifth stage, whilst in other 

 cases from the lightest individuals of the fourth 

 stage there arise all the possible modifications of 

 the fifth stage. Further details may be omitted : 

 the negative result cannot cause any surprise, as 

 it is a necessary consequence of the continued 

 crossing that must take place. 



We thus see that the three chief stages of 

 development (larva, pupa, and imago) actually 

 change in colour independently of each other, the 

 single stages of the larval development being 

 however in greater dependence upon one another, 

 and being connected indeed in such a manner that 

 a new character cannot be added to the last stage 

 without being transferred in the course of time to 

 the preceding stage, and at a later period from this 

 again even to the youngest stage, supposing it not 

 to be previously delayed in the course of its trans- 

 ference by unknown opposing forces. On this 

 last point, however, the facts at present available 

 do not admit of any certain decision. 



But why do the individual larval stages behave 

 in this respect so very differently to the chief stages 

 of the whole development ? why are the former 

 so exactly correlated whilst the latter are not ? 

 If new characters have a general tendency to be- 

 come transferred to the younger ontogenetic stages, 

 why are not new imaginal characters first trans- 

 ferred to the pupa, and finally to the larva ? 



