252 Stiidies in the Theory of Descent. 



such an extreme multiplicity of forms is interesting, 

 since, so far as I know, polymorphism to this 

 extent has not been observed in any insect. 



The theoretical bearing of this polymorphism 

 will be treated of subsequently. It is not in any 

 way connected with a more advanced development 

 of the markings, since M. Stellatarum shows in 

 this respect a very low state of development. This 

 species displays only two stages : (i), complete 

 absence of all markings; and (2), a simple subdorsal, 

 with dorsal and spiracular lines. We must there- 

 fore admit that the phyletic development of the 

 markings has for a long time remained at a stand- 

 still, or, what expresses the same thing, that the 

 marking which the adult larva now possesses is 

 extremely old. 



In order to complete my observations on M. 

 Stellatarum, I now add some remarks on the 

 pupa, the colour variations of which it appeared of 

 importance to investigate, owing to the extraordi- 

 nary variability of the caterpillar, The pupa varies 

 but very slightly ; the ochreous yellow ground- 

 colour sometimes passes into reddish, and some- 

 times into greenish ; the rather complicated black- 

 ish-brown marking of streaky lines is very con- 

 stant, [especially on the wing portions, being at 

 most only more or less strongly pronounced. The 

 minute colour variations of the pupa therefore have 

 no connection with the colour of the caterpillar, 

 both green and brown larvae furnishing sometimes 



