THERETRA PORCELLUS. 101 



larvae turned brown ; I had not one that showed any trace of the 

 previous green colouring. The fullfed larva was, when walking. 

 55mm. long, less than 50mm. when at rest, smooth and plump, 

 stoutest at segments 5 and 6, thence tapering very rapidly to the 

 head, which was very small, and with 2 and 3 retractile into 4 ; 

 segment 12 tapers a little, 13 rapidly; on 12 a small two-pointed 

 wart o*5mm. high, the skin showing eight not distinct folds in 

 each segment. The colour ashy-brown, freckled with black, the 

 front of each segment being paler and bearing larger freckles, so 

 as to look like a transverse band there ; the head ashy ; on 2 — 4 

 the ground is pale buff, the markings dark brown ; a thin dark dorsal 

 line; a buff subdorsal stripe outlined in black; 5 and 6 bear each 

 on the subdorsal level a round spot, that on 5 being the larger; 

 on 5 the spot is lilac with purple-brown centre, on 6 it is paler 

 lilac with brown centre bearing a yellow dot; both these spots are 

 surrounded with strong dark borders, making them very conspicu- 

 ous. The wart on 12 a little paler than ground, but not conspicuous; 

 the spiracles pale, indistinct ; the belly unicolorous, of a pale livid hue 

 with pinkish tinge (Hellins). Buckler figures (Larvae British Moths, 

 ii., pi. xxvi., fig. 1 b) the fullgrown larva of the green form, also (loc. 

 cit., figs. 1, i^) two fullgrown larvae of the dark form, and (loc. cit., fig. 

 1a) the larva, before, the last moult. 



Variation of larva. — The larvae of this species are green 

 when young, but a very large percentage becomes brown at the 3rd 

 ecdysis, although a few retain their green coloration. Ochsenheimer, 

 in 1808, noticed that adult green larvae were rare, most being 

 black or blackish-grey. Weismann notes (Studies in Theory of 

 Descent, p. 186) that, although he twice reared this species (17 

 larvae in all), in no case had he a larva which remained green 

 throughout to maturity, and the green form as adult appears to 

 be rare. Meldola notes (loc. cit., p. 188, footnote) instances 

 of the green form occurring in Surrey, Kent, &c, but they ap- 

 pear to be infrequent. Hellins says that a larva which turned 

 brown at the third moult had the subdorsal line dingy buff. The 

 spot on the 1st abdominal segment' had a reddish centre and a 

 dark brown edge ; the spot on the following segment white. He 

 also describes the brown form when fullfed (see supra). Buckler 

 figures (Larvae Brit. Moths, pi. xxvi., figs. 1 and ic) two very 

 different-looking examples of the brown form. 



Development of larval markings. — First instar ; The larvae 

 on first hatching measure 3*5mm. in length, are of an uniform light 

 green colour, with a fine white transverse line on the posterior 

 edge of each segment, precisely similar to that which appears in 

 the 2nd stage of E. elpenor. They resemble the latter species 

 still further in showing a fine white subdorsal line, which can 

 easily be recognised by the naked eye (fig. 24). Although the 

 adult larva is distinguished from all other known species of Choero- 

 campa by the absence of a caudal horn, a distinct but very small 

 one is nevertheless present at this first stage, and is, indeed, re- 

 tained throughout the entire course of development, but does not 

 increase further in size, and thus, gradually, becomes so small in 

 proportion to the size of the caterpillar that it may be entirely 

 overlooked. The first moult takes place after 4-5 days. Second 



