TUE GENUS SMERINTHUS. 17'J 



sex, except in one female, which had a group of small bristles on one 

 hind-wing only. No doubt this was simply an instance of reversion, 

 the frenulum being as a rule altogether Avanting in this species. 



A consideration of all the different characters i)resent in the several 

 stages leads me to think that S. tiliae is the oldest form, and that S. 

 ocellattis, though its habit and food are ver}'^ different, as is also the 

 coloration of the imago, is not really so widely removed from S. tiliae 

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

 S. popnli, on the other hand, is, I believe, much farther removed from 

 S. ocellutns than is usually thought to be the case ; it seems to have 

 developed right away from the others, and to have lost many of the 

 ancestral features that they retain. The similarity of the eggs and of 

 certain characters in the young larvaj of S. tiliae and S. ocellatns, and 

 the wide divergence of .S'. poptili in these stages, will be apparent from 

 a stud}^ of the tables that 1 have passed round. I am well aware that 

 the adult larvae of S. ocellatns and S. popnli are often diificult to 

 distinguish ; but the likeness is really only a general one, and probal)ly 

 arises as much from the similarity of their food-plants and of the 

 dangers to which they are exposed as from actual relationship. When 

 we compare the imagines, the resemblance between S. tiliae and 

 S. ocellatns, as regards the shape and markings of the wings, is very 

 close, while S. popmli is entirely different in both respects. One very 

 stable and, perhaps, im})ortant marking that S. ocellatns and (S'. poptili 

 have in common is the white lunule on the margin of the discoidal cell 

 of the fore-wings ; but though no trace of this is i)resent in any of the 

 specimens of S. tiliae that I have seen, a very similar mark may be 

 noticed in S. liyustri, albeit in this species it is black instead of white. 

 Mr. F. N. Pierce, of Liverpool, has been good enough to make prepara- 

 tions of the genitalia for me, and writes thereupon as follows : — " I 

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

 strong, and I have only succeeded fairl}" well. As regards size, those 

 of S. popnli and S. tiliae seem much nearer ; but in structure there is 

 no doubt that those of S. ocellatns and S. popnli are nearer to each other 

 than either of them are to those of aS. tiliae. I am much struck with 

 their strength in S. ocelhttns compared with what obtains in «S. populi." 

 From Mr. i'ierce's remarks it will be seen that the evidence of relation- 

 ship afforded by the genitalia is not in accord with that furnished l)y 

 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. 



Hybrids. — The occurrence of hj'brids between S. ocellatns and 

 S. popnli is a fact that has always had a certain amount of fascination 

 for me. Up to the present my attempts to cross the two species have 

 only yielded me a very poor series of the former, but I shall try again. 

 The literatui'e of the subject is not extensive. The earliest note 1 have 

 been able to find is one l)y Mr. House in Trans. Eat. Soc. Land, for 

 1842. Mr. House oljtained five batches of eggs from S. popnli im- 

 pregnated by S. ocellatns, and one batch from S. ocellatns impregnated 

 by S. popnli, but only •ii) eggs fronr one of the former liatclies proved 

 fertile. Fi'om tliese he reared I'J larvae, which pupated in July. 

 Twelve moths emerged in August, the other seven pu[ia' going over 

 the winter. Of the imagines, he says : — " The power of reproduction is 



