70 Mr. P. Cameron on the 



the larva of S. ocellatus — one feeding on Salix triandra, 

 without markings, and another on Salix viminalis, with a 

 double row along the side. We can scarcely suppose that 

 the marks serve no useful purpose ; and we have in the 

 case of Dellephila Hippophaes a very good illustration of 

 similar marks simulating objects — the berries — found on 

 the food-plant. There is another circumstance which 

 favours my view, the circumstance, namely, that the three 

 principal food-plants of our species of Smerinthus — Tilia, 

 poplars, and willows — are much infested on the leaves with 

 fungi (as the poplar), or, as Avith all three, with mites 

 (Phytopus), which form on the leaves little galls of from 

 1 to 3 ' in length, and usually of a brownish-red colour ; 

 while they are, like the fungi, very common, and have a 

 wide distribution. On a willow {Salix aurita) close to 

 where I discovered the caterpillars, I found many mite- 

 galls on its leaves, and compared them with the markings 

 in the caterpillar. Many were larger, and many smaller, 

 while the colour was scarcely so bright in most cases, but 

 still at a distance of a yard or two the resemblance was 

 considerable, and could only be detected by a practised 

 eye. I do not know if the spotted caterpillars are found 

 only on infested trees, or the contrary ; what I contend 

 for is, that these and similar excrescences, being so common 

 on the food-plants (and indeed on most plants near those 

 frequented by the larvas), the reddish markings serve to 

 protect them. 



In the above-mentioned caterpillar of >S'. populi, the red 

 spots were fully larger than those in Weismann's figure 

 of Deilephila Hippophaes, * and they were the same in 

 number (G) ; the spiracles too were surrounded with red ; 

 hut these red blotches, though more numerous, were 

 scarcely so large as those on the upper roAv, although con- 

 spicuous enough. 



My observations have shown too, I think, that they do 

 aid in concealing the larva on an infested tree. The fact 

 of the spots appearing late in life may be owing to the 

 caterpillar's increased size rendering it more conspicuous 

 than it was when younger, and, consequently, standing 

 more in need of additional means to aid concealment. It 

 may be added that Hijjpophae rhamnoides, the food-plant 

 of Beilephil a Hippophaes, has a Phy topics] attached to it ; 



* Descendenz — Theorie, ii., pi. iv., f. 59. 



f cf. Rudow. Ilflnnzen-gallen Nonkleutsclilamls, p. 173. 



