480 BRITISH LEPIDOPTERA. 



somewhat darker. Length 12mm. Fourth ins tar : The third 

 moult (after another four days) likewise brings only a change ot 

 colouring, which is of such a nature that the caterpillar becomes 

 dimorphic. At the same time that peculiar roughening of the skin 

 takes place, which has been designated as shagreening. The colour 

 is now (1) light grass-green in some specimens, (2) dark green in 

 others. In these last, the subdorsal line is edged above with dark 

 brown, and the spiracles are also of this colour. Length 17mm. 

 Fifth instar : Four days later the fourth moult takes place, and 

 the dimorphism then becomes a polymorphism, in which' five chief 

 types can be distinguished : 



1. Light green (pi. iii., fig. 7); dorsal line blackish -green, strongly marked; 

 subdorsal line broad, pure white, edged above with dark green ; spiracular line 

 chrome-yellow ; horn black, with yellow tip and blue sides ; spiracles blackish- 

 brown with narrow yellow border ; legs and extremities of prolegs vermilion -red. 



2. Blackish-brown (pi. iii., fig. 6) ; head and prothorax yellowish-brown ; 

 markings the same as 1. 



3. Blackish-green or greenish-black (pi. hi., figs. 10-11); subdorsal line with 

 blackish-green border above, gradually passing into a light green ground colour ; 

 spiracular line chrome-yellow ; head and prothorax greenish-yellow. 



4. Light green (pi. iii., figs. 4 and 12); dorsal line quite feeble; subdorsal 

 broad, only faintly edged with dark green ; subspiracular line faint yellowish ; head 

 and prothorax green. 



5. Brownish-violet (pi. hi., fig. 8) ; the black dorsal line on a reddish ground 

 either narrow or broad. 



From these five varieties we see that the different types do not 

 stand immediately next one another ; they are, in fact, connected 

 by numerous transitional forms, the ground colour varying greatly, 

 being dark or light, yellowish or bluish (compare figs. 4, 5, 7 and 

 12). The markings remain the same in all, but may be of very 

 different intensities. The dorsal line is often only very feebly 

 indicated, and the subdorsal line is frequently but faintly edged ; 

 the latter is also sometimes deep black above and bordered rather 

 darkly beneath, the sides then being of a dark green, often with 

 blackish dots on the yellow spiracular line (fig. 5), this likewise being 

 frequently edged with black. Only the horn and legs are alike in 

 all forms. The green ground colour passes into blackish-green, 

 greenish, or brownish-black, and again from reddish-brown to lilac 

 (fig. 3), this last being the rarest colour. We have here no sharply 

 distinct forms, but fi\e very variable ground colours connected by 

 numerous intermediate modes of coloration. I am in possession of 

 an observation which tends to show that the different colours have, 

 to a certain extent, become fixed. 1 found a brown caterpillar, the 

 front five segments of which were light green on the left 

 side, and the fifth segment brown and green mixed (pi. iii., 

 fig. 9). Such parti-coloration can evidently only appear where we 

 have contending characters which cannot become combined. 

 From this observation, I conclude that some of the chief varieties 

 of the larva of stellatarum have already become so far removed from 

 one another that they must be regarded as intermediate fixed forms, 

 the colours of which no longer become fused together when they 

 occur in one individual, but are developed in adjacent regions. 

 Other facts agree with this conclusion. Thus, among the 140 adult 

 larvoe which I bred from the batch of eggs above mentioned, the 

 transition forms were much in the minority ; there were 49 green 



