SMERINTHUS HYBR. HYBRIDUS. 457 



always bluish in colour, never yellow or reddish as in populi. All 

 the larvae possessed the horizontal prolongation of the first oblique 

 stripe on the neck, a characteristic which also only belongs to populi 

 larvae. 



Differences between adult larvae of S. hybr. hybridus, S. 



ocellata, and A. populi. — v i) S. hybr. hybridus and S. ocellata. — 



Head of S. hybr. hybridus smoother, and not so pointed ; yellow lines 



down face much broader. Body not so long and graceful; the subdorsal 



stripes much weaker, the oblique stripes not so strong ; slight traces 



of small oblique stripes just above the bases of prolegs i, 2 and 3 



(these are altogether absent in S. ocellata). Caudal horn : yellowish 



at upper end. Spiracles : not so large or dark ; 1st and 2nd pairs 



of prolegs are retractile, but to a less extent than in S. ocellata. 



Resting habits differ as a rule. (2) S. hybr. hybridus and A. populi.- — 



Head of ^S. hybr. hybridus taller and more pointed. Body : longer and 



not so dumpy. Oblique stripes : rather broader as in the larva of 



S. ocellata, the stripes are due rather to colour than structure, the 



1 st no stronger than the following — 2nd to 5th ; the 7th runs 



forward to front of 4th pair of prolegs (as in S. ocellata). Small 



oblique lines above base of prolegs present, but much fainter 



than in A. populi. Caudal horn : sky-blue in colour at base. (3) 



General notes: In its general appearance the larva, in the 1st and 



2nd stages, approaches S. ocellata rather than A. populi ; in 3rd 



and early part of 4th stages it has a greater resemblance to A. 



populi ; when fullfed it veers back again towards S. ocellata. A 



very similar change takes place in the larval life of A. populi, 



though, perhaps, this is not quite so marked as in the hybrid. It 



is in the middle stages (2nd and 3rd) that this larva attains its 



greatest distinctiveness ; in the first and last stages the difference 



between it and the larva of S. ocellata not being nearly so sharply 



contrasted, and this departure and return is in no way due to the 



development of S. ocellata, which does not greatly differ in appearance 



throughout its ontogeny. In the shape and structure of the head, 



and the markings on its body, the hybrid larvae were remarkably 



constant. I looked with especial care for any individual variation 



or difference in the oblique stripes, which it seemed not unlikely 



might vary in the direction of A. populi, by a strengthening of the 



1 st, but in no case was there the slightest tendency in this direction. 



Throughout my notes I have made comparisons between the 



hybrid larvae and those of the parent species, but in some 



characters the agreement with M. tiliae is as close as, or closer 



than, that with S. ocellata and A. populi, and where this agreement 



is present, as, for instance, in the colour of the processes at the 



apex of head, we have, I think, conclusive evidence that this 



was their original appearance. The larvae were very delicate, 



more especially during the early stages, the moulting periods 



being the most critical of all. The less robust appeared to have 



great difficulty in getting rid of their old skin; I assisted them off 



with their old clothes in several instances, but, alas, in no case 



did my help prove of any avail, for they died in spite of my 



philanthropic efforts. I suspect the difficulty really consists in 



drawing out the old linings of the tracheae, the rough assistance 



one is able to render, probably results in breaking them away 



