amorphiNjE. 385 



as a superficial knowledge of the two species might lead us to 

 suppose. A. populi, on the other hand, is, I believe, much farther 

 removed from S. ocellala than is usually thought to be the case ; 

 it seems to have developed right away from the other British 

 species, and to have lost many of the ancestral features that they 

 retain*. The similarity of the eggs and of certain characters in 

 the young larvae of M. tiliae and S. ocellata, and the wide divergence 

 of A. populi in these stages, are apparent on close comparison. I 

 am well aware that the adult larvae of S. ocellata and A. populi 

 are often difficult to distinguish, but the likeness is really only a 

 general one, and probably arises as much from the similarity of 

 their foodplants and of the dangers to which they are exposed as 

 from actual relationship. When we compare the imagines, the 

 resemblance between M. tiliae and S. ocellata, as regards 

 the shape and markings of the wings, is very close, while 

 A. populi is entirely different in both respects. One very 

 stable and, perhaps, important marking that S. ocellata and 

 A. populi have in common, is the white lunule on the margin of 

 the discoidal cell of the forewings ; but, though no trace of this is 

 present in any of the specimens of M. tiliae that I have seen, a 

 very similar mark may be noticed in S. ligustri, albeit in this species 

 it is black instead of white. Pierce, of Liverpool, who has made 

 preparations of the genitalia writes thereupon as follows : ' I 

 found them very difficult to manage, as they were so large, thick 

 and strong, and I have only succeeded fairly well. As regards 

 size, those of A. populi and M. tiliae seem much nearer, but in 

 structure there is no doubt that those of S. ocellata and A. populi are 

 nearer to each other than those of either of them are to those of M. 

 tiliae. I am much struck with their strength in ,5. ocellata compared 

 with what obtains in A. populi? From these remarks it will be 

 seen that the evidence of relationship, afforded by the genitalia, is 

 not in accord with that furnished by other characters. I am not 

 altogether surprised at this, as the genital organs would probably 

 be among the first to undergo modification in a new species, and 

 they are probably not so valuable a guide to the relationship 

 between well established species as to the distinction between 

 species that have all their superficial characters in common." 

 Later Bacot writes (Joe. cit., ix., pp. 145 — 146): "The pupa of 

 Satumia pyri is not unlike that of Mimas tiliae in shape, only 

 rather wider in regard to its length, and, of course, differing at head 

 and anus. In general shape and appearance, omitting the antenna- 



* In those characters which are considered to be ancestral, S. ocellata 

 and M. tiliae show more agreement than does either with A. populi. It is probable 

 that M. tiliae first branched from the stirps which gave rise to our three British 

 species, S. ocellata being very probably nearer to A. populi, in the sense that 

 they formed an ocellata + populi branch, after tiliae had separated as a distinct 

 species ; but since this branch was thrown off, and after ocellata and populi had 

 separated from their common ancestral form, the specialisation of the latter has 

 advanced so far that it has lost many of the characters which the other two species 

 retain. The reference [supra] to M. tiliae as the oldest form must be taken from 

 this standpoint. It has itself specialised no doubt in coloration, pattern, and in the 

 larval form, but, at the same time, it is more Sphinx-like than either of the other 

 species. It is, of course, possible to consider this as an instance of parallel 

 specialisation (Bacot). 



