THE GENUS SMEllINTHUS. 175 



(or last two) pair of prologs, assumiug an upright attitude, with the 

 fore part of the hocly raised and the head drawn hack. In this position 

 its resemblance to a leaf is very pei'fect, and the reason for the with- 

 drawal of the unused prolegs is apparent, as, if not withdrawn, they would 

 break the regular leaf-like ontline. Occasionally I have found larvae at 

 rest on the uiid-ribs of partially eaten leaves, and in that position they 

 do not raise the fore part of the body, and they use all the prolegs. 



The variation of the full-grown larvfe is almost parallel with that 

 of S. popnii: the oblique stripes are, however, usually broader and 

 whiter, thougli sometimes, in the yellow forni, they are as yellow and 

 nearly as narrow as in *S'. popnii. Larvae are sometimes met with which 

 have traces of an 8th obli(pie stripe, and Mr. Poulton mentions one 

 which had a 9th as well. One that I bred this year showed a tendency 

 to darken before pupation in the same way that those of S. tiliae and 

 S. U(jnstri do. The food-plants given are blackthorn, apple, willow, 

 sallow, poplar, aspen and wild })lum. 



S. popnii. — The larva of this species makes only three moults, while 

 those of the other two make four. Whether this is always the case I 

 cannot say. Possibly some broods may have four moults, others only 

 three. Dr. Chapman states that some larvae of Moma orioii have four 

 moults, others five, and that this is not a sexual difference, as is the 

 extra moult in the female larva of Orgi/ia antiqna. 



The larvje of -S'. popidi, like those of S. ocellatna, vary considerably 

 in their later stages, ranging from dull green or sage-green to (piite a 

 bright yellow. The spiracles are often surrounded b}^ a i-ed spot, and 

 it is not uncommon to get larvaj with an entire or partial subdorsal 

 row of similar spots. These spots are said to simulate the small red 

 galls so often found on willow and poplar leaves. In one larva that I 

 bred this year the spots of the lower row were absent from the thoracic 

 segments, Avhilst those of the upper row were present on those segments. 

 I used to liave a notion that the different forms were from diffeient 

 broods, chiefly because I had usually found the dull-green forms on 

 black poplar and the bright ones on Lomljardy poplar, sallow or willow. 

 It is true that I have occasionally found the latter on black poplar, but 

 I do not remember ever taking the dull forms on Lombardy poplar. 

 This year, however, I bred both forms from eggs laid by a single female, 

 and Ur. Buckell has had the same experience. 



The young larvfe have very similar habits to those of ,S'. ocellatns, 

 but, as they get older, the position in which they rest is very different ; 

 this is nearly always with the head downwards, and although the fore 

 part of the body is raised, as in S. ocellains, the head is curved inwards 

 towards the leaf or twig ; they will grasp the stalk of a leaf with their 

 anal claspers only and hang down behind it, and it is quite remarkable 

 how small a sallow leaf suffices to hide a full-fed larva. On poplars 

 I have frequently noticed them, when they have eaten half the leaf, so 

 resting as to represent the eaten portion themselves, and they are then 

 so well protected that, with any wind, it would I think be impossible 

 to detect them. I have noticed that the larvie are much easier to find 

 on misty mornings and before the sun is u]). Probably the explana- 

 tion of this is, that inl)right sunsliine the lights and shadows are much 

 stronger, and conse(iuently the sliglit difference in tint between tlie 

 larva and the leaf is not so noticeable. Tlie same fact holds good witli 

 S. oceUdtitfi, and 1 think tliat, as a rule, the jjrotective coloration of 

 larvae is most perfect in sunlight or in full daylight. 



