Phylctic Parallelism in Metamerpku Species. 405 



combinations which are theoretically conceiv- 

 able. 



(i.) There are species which possess a high 

 decree of constancy in all three stages, such, for 

 example, as Linienitis Camilla, Pieris Brassica? 

 SpJUnx Lignstri, and Euchelia Jacobaa. 



(2.) There are species showing a high degree 

 of variability in all three stages. This case must 

 be of rare occurrence, as I am only able to adduce 

 Araschnia Prorsa-Levana, a fact which arises 

 from the circumstance that the pupal stage is, as a 

 rule, but seldom variable. 



(3.) There are species which are variable in two 

 stages and constant in the third. To this class, 

 for example, belongs Smerinthus Tilia, of which 

 the larva and imago are very variable, whilst the 

 pupa is quite constant. The same is the case 

 with Lasiocampa Pint, the well-known fir moth. 

 Many butterflies show this same phenomenon in 

 other combinations, such, for instance, as Vanessa 

 Urtica and Polychloros, in which the larva and 

 pupa are very variable, and the imago very con- 

 stant. In a less degree the same is also the case 

 with Vanessa Atalanta, whilst in Pieris Napi the 



1 [The slight variability in the colour of this pupa, opens up 

 the interesting question of the photographic sensitiveness of 

 this and other species, which is stated to cause them to 

 assimilate in colour to the surface on which the larva under- 

 goes its final ecdysis. Some experiments upon this subject 

 have been recorded by Mr. T. W. Wood, Proc. Ent. Soc. 1867, 

 p. xcix, but the field is still almost unexplored. R.M.] 



