STRYMON PRUNI. 209 



head. It is thickly covered with long pale brown hairs. The 

 prothoracic spiracles are placed low down, one on each side, just 

 in front of the segmental incision that separates the prothorax 

 from the mesothorax. The mesothorax is wider than the prothorax, 

 extends back considerably, and is somewhat protuberant, the two 

 transverse subsegmental divisions apparent on the dorsum, and 

 suggesting the mesothorax of the pupa. The metathorax is wider 

 transversely, but very narrow from front to back. It is round the 

 centre of this segment that the silken girth is placed at this stage, 

 although it slips back to the 1st abdominal when pupation takes place. 

 Abdomeyi : Dorsally, the 1st abdominal segment is narrow from front 

 to back, and without any special armature. (It may be readily 

 distinguished, however, by its conspicuous spiracle.) The 2nd, 3rd, 

 4th, 5th, and 6th abdominal segments have a raised ridge on each side 

 of the mediodorsal area. These are broken up by the segmental 

 incisions, and, owing to the stretched condition of the larva in this 

 stage, it is seen that the portions of the ridge do not extend to the 

 anterior subsegment of the segments on which they are placed. 

 This suggests, also, that the backward direction which each portion 

 of the ridge takes, has been brought about to make it appear as 

 complete as possible when the larva is crawling, whilst the absence of 

 the ridge on each anterior subsegment gives freedom of movement to 

 the larva. The upper edges of the ridges are of a purplish-red colour, 

 outlined with pale yellowish externally, the purplish portions being well- 

 supplied with purplish-coloured hairs, the yellowish portion with pale 

 hairs. Although the ridges practically end with the 6th abdominal 

 segment, the median furrow is theoretically extended to the anal 

 segment, where the ridge crops up again as a raised, median, purplish- 

 red, dorsal, terminal point. The furrow is but very little darker than 

 the ground colour. The anal segment bears some general resemblance 

 to the prothoracic segment, in its flat, lip-shaped appearance. 

 Laterally : The sides of the caterpillar are separated from the venter 

 by a slightly tumid, longitudinal, marginal ridge, well supplied with 

 long whitish hairs, whilst above this, and parallel with it, is a pale, 

 sharply defined, longitudinal, subspiracular line, which extends the 

 whole length of the body. The segmental incisions are well denned 

 and pale, and the points, where the segmental incisions cut the sub- 

 spiracular lines, are very prominent. The dull orange spiracles are very 

 conspicuous, and placed very high on the sides, about half-way 

 between the lateral (subspiracular) line and the dorsal ridge. The 

 larva changed to a pupa during the night of May 27th (Tutt). On 

 June 1st, 1907, I received three larvae of S. pruni, already fixed for 

 pupation. They are notable for the great increase in height of the 

 larva. One is fixed on the tin, the other two on leaves (of sloe). 

 They measure 11mm. long, 4*7mm. and 4.3mm. wide, and 5-8mm. high, 

 at 3rd abdominal segment. The girth passes over between the thorax 

 and abdomen. Seen laterally the larva has the 3rd, 4th, and 5th 

 abdominal segments forming angular serrations dorsally, the 2nd and 

 6th very slightly so. From the 6th abdominal segment to the end is 

 nearly a straight line down the dorsum. The four serrations are on a 

 curve. From the 2nd abdominal segment to the mesothorax is a fairly 

 straight line ; from front of mesothorax down prothorax is a line 

 2*3mm. long, about vertical to surface of leaf. The colour is vivid 



