388. BRITISH LEPIDOPTERA. 



a little longer than n A. populi*. The horns are of almost exactly the same length 

 in all three species, viz., 2-2mm., and terminate in two hairs, each about o-i^m. 

 long. S. ocellata has a larger number of long hairs on it than the others. On 

 M. tiliae the fine hairs are much shorter than on the other species, and with 

 insufficient magnification look as if they were merely simple hairs ; they are, 

 however, forked as in the other species. The horn of A. populi is rather shorter 

 than in the others. Fullgrown (in 1st instar . — When the three larvae are fullgrown 

 in this (first) instar, they present decided differences. S. ocellata is rather over fin. 

 long, and of much the outline and proportion of the larva in its last instar. A. 

 pnpuli is much the same, but appreciably longer and a little more slender, whilst M. 

 tiliae is longer and more slender to a remarkable degree, being almost exactly *5in. 

 long, but not more bulky than the others. The markings also differ. A. popitli has 

 the oblique lines bright yellow on a green ground, the two colours only, each 

 definite and distinct, and with no intermediate shades ; half-way down these there 

 is a longitudinal yellow line, of about the same width as the oblique lines, and of the 

 same colour; this extends right up to 1st segment. The dorsal tubercles of the 

 thoracic segments are also yellow. The dorsal ends of the oblique lines are indistinct 

 on the two posterior subsegments, and appear to terminate with square ends (on bth 

 subsegment) at some distance from the dorsal line. S. ocellata is very similar, but 

 the anterior margin of the oblique lines is sharp, whilst the posterior rather shades off 

 into the ground colour ; the upper margin of the longitudinal line does the same, and 

 between them they invade nearly the whole of the ground colour in the triangle 

 between them ; the oblique lines further continue backwards just below the dorsal line, 

 along the whole of the next segment behind, and so cut off a very definite dark green 

 dorsal line ; below the longitudinal line, the oblique ones are narrower and more 

 definite, and stretch forwards for two or three subsegments of the preceding 

 segment, but less distinctly than they do in A. populi for nearly the whole segment. 

 S. ocellata, instead of the two colours yellow and green, has deep blue-green (dorsal 

 line), green, yellowish-green, and yellow (and the red horn). M. tiliae has the 

 longitudinal line much broader than in either of the others, and at first sight the 

 oblique lines are wanting ; they may, however, be traced as very narrow Hues, most 

 visible below the longitudinal line, but also through it. The longitudinal line is much 

 less a line than in the others, but a broad shade, fading above and below into 

 the ground colour. The dorsal line is dark blue-green. The longitudinal line 

 is whitish- or yellowish-green rather than yellow. The whole larva of more 

 uniform aspect than the others, and of a bluer and whiter general tone. 

 Second instar. — In M. tiliae, the larva, in colour, etc., is not very different from 

 that of the first instar, but the subsegments have now each one row of rather large 

 mammillae (Poulton's " shagreening " z=z cone-shaped bases of secondary hairs) 

 solarge that their bases occupy the whole width of the subsegment ; at the date of moult- 

 ing and before the larva has grown, these are tall and end in a hair or spine, slightly 

 thickened at the end, and carrying several fine points. They are no longer bifurcate 

 or fish-tail hairs, but these are still represented by a few very small hairs between 

 and beside the mammillae. In A. populi, second instar, the larva is green, slightly 

 paler horn, ist and last oblique line much stronger than others, longitudinal line 

 narrow and very distinct. It presents the same mammilla? as in that of M. tiliae, 

 ranged in one row along each subsegment, but a condition hardly observable in 

 ill. tiliae is here very pronounced, viz., that the mammillae are yellow on the green 

 ground colour, and are very large and pronounced in the yellow oblique and longi- 

 tudinal lines, and indeed form these lines, whilst elsewhere they are much smaller, 

 and, in the greenest areas, are practically absent. The hairs with which they are crowned 

 are shorter than in M. tiliae and have the same thickened spiculate summit. The 

 very small bifurcate hairs distributed amongst the mammillae are, owing to the 

 open spaces, more numerous than in M. tiliae. In S. ocellata, second instar, the 

 conditions resemble A. populi in the great variations in the size of the mammilla;, and 

 the way they form the markings. The mammillae are nearly white, their terminal 

 hairs are as finely bifurcate as in the first instar, and the fine intermediate hairs are so 

 similarly. The head in first instar is rounded, in the second it possesses in S. ocellata a pair 



* Perhaps it would be more accurate to say that the forked hairs of the 

 smaller sort do not differ in the three species quite so much as described above, 

 but that they do differ in the directions stated, fairly fish-tailed forms occur among 

 the smaller hairs of S. ocellata, the fine acutely branched form desciibed is 

 distinctive of S. ocellata. but affects the larger hairs. The larger hairs of A. populi 

 and J/, tiliae are not bifurcate but only a little thickened and slightly spiculate 

 at top. 



