1886.] Larva of Smerinthus ocellatus and its Food-plants. 163 



whitish-green, and I think that a white larva is better protected when 

 resting on the under side of the leaf than a yellow larva would be, 

 although this is often true in the case of trees v/hich are known to 

 produce yellow larva?. Again the leaves are large as a rule, and so 

 the larva? are advanced when they rest on the stem, and even then the 

 arrangement of the leaves and the position of the larva cause the under 

 side to contribute most colour to the immediate environment. I have 

 already mentioned that the bright yellow, red-spotted larva captured 

 in 1884 upon crab, var. acerba, was upon a tree with exceedingly 

 small leaves. Furthermore, in this variety the leaves are extremely 

 variable in size upon different parts of the tree. But although the 

 conditions mentioned above may have conduced towards the fact that 

 my bred larvae fed upon this plant became so white, I cannot but 

 think that such a result was largely due to their strong hereditary 

 tendency towards this colour, for the crab cannot compare with, 

 ordinary apple in the whiteness of the under sides of the leaves, nor 

 is it in this respect equal to Salix viminalis, Smithiana, or even 

 cinerea. I think that this food-plant more than any other requires 

 further experimental work with larvae of all varieties of hereditary 

 tendency, but it is very unfortunate that the larvae do not seem to 

 thrive upon the plant, at any rate in confinement. 



Another great difficulty is, I think, completely explained by the 

 above-mentioned consideration. I mean the fact that bred larvae 

 tending strongly towards white, became intermediate in 1884 and in 

 many cases in 1885 when fed upon the large-leaved variety of Salix 

 viminalis (for T have always fed my larvae upon this variety). In 

 order to obtain the best leaves I have to walk to the Cherwell and 

 take a boat ; and as this is not always convenient, I bring home and 

 give to the larvae a great quantity. The leaves being very long and 

 crowded in the glass cylinders in which the larvae are kept, their 

 natural arrangement is entirely altered, so that the upper sides are 

 presented to the larvae to a much greater extent than happens on the 

 tree. The result is to affect the environment of the larvae upon the 

 leaves as well as those upon the stem, for in the former case the 

 upper sides of other leaves must be often crowded close up to the 

 under side of the one upon which a larva is resting. Furthermore, 

 the leaves do not last so long without withering as upon the trees in 

 the open air, and therefore the larvae are frequently compelled to 

 wander on to fresh leaves, and in so doing they must be affected 

 by the colour of the upper as well as the under sides. In the future 

 it would be well to breed some larvae in large cases which would hold 

 the twigs without overcrowding, and would permit the leaves to fall 

 naturally. In the case of apple the arrangement of the leaves has 

 not been disturbed in the cylinders, because I can get the twigs in 

 my garden, and because the leaves are of a more manageable shape. 



