76 BRITISH LEPIDOPTERA. 



and on the front three segments, whilst on the 3rd segment the 

 formation of another eye-spot commences to be plainly perceptible by a 

 local deposition of black (fig. 23). This third spot does not, how- 

 ever, become completely developed, either in this or in the last stage, 

 but the subdorsal line remains continuous on the three front segments. 

 Among other changes at this stage, there occurs a considerable 

 shortening of the caudal horn, which, at the same time, loses its 

 beautiful black and red colours and becomes brownish, The two 

 large eye-spots have now nearly attained complete development. The 

 kidney-shaped white spot has become entirely surrounded by black, 

 and, on the brown, red, and yellow tints present in this spot during 

 the last stage, a nearly black spot has been developed — the pupil of 

 the eye* (fig. 33). In this 5th stage the larva attains a length of 

 6cm., after which the 5th moult takes place, the larva becoming ready 

 for pupation in the 6th stage. No striking changes of colouring 

 or marking occur after the present stage, but only certain unimportant 

 alterations, which are, however, of the greatest theoretical interest. 

 Sixth stadium f : In this stage the eye-like appearance of the spots on 

 the front segments becomes still more distinct than in the 5th stage ; 

 at the same time these spots repeat themselves on all the other 

 segments, from the 6th to the nth, although certainly without pupils, 

 and appearing only as diffused deep black spots, of the morphological 

 significance of which, however, there cannot be the least doubt. 

 They are situated in precisely the same positions on the 6-1 1 seg- 

 ments as those on the 4th and 5th — near the front, and above and 

 below the subdorsal line. A feeble indication ot the latter can often 

 be recognised (fig. 23). In all dark brown specimens the repeated 

 spots can only be detected in a favourable light and after acquiring an 

 intimate knowledge of the caterpillar, but, in light brown and green 

 specimens, they appear very sharply defined. There is one other new 

 character never observed at an earlier period than the 6th stage — 

 viz., the small dots which appear in pairs near the posterior edge of 

 segments 5-1 1. These dots cannot have been developed from the 

 subdorsal line, as they are situated higher than the latter. Their 

 colour varies according to the ground-colour of the caterpillar, but it 

 is always lighter, being light green in green specimens, dull yellow in 

 those that are light brown, and grey in the blackish-brown cater- 

 pillars. These " dorsal spots " are chiefly of interest because they are 

 present in the larva of TJieretra porcellus, in which species they appear 

 one stage earlier than in Eumorpha elpenor v Weismann, Studies in the 

 Theory of Descent, transl. pp. 177 et sea.). 



Comparison of adult larvae of Eumorpha elpenor and 

 Theretra porcellus. — [The larva of E. elpenor is the younger, 

 so that the larvae are almost equal as regards size. Both larva? 

 are of the dusky form.] General coloration : The larva of E. 

 elpenor is of a more inky hue than that of T. porcellus, which 



* In ordei to establish a definite terminology for the different portions of the 

 eye-spot, the pupil is designated the " nucleus," the light ground on which the pupil 

 stands the "mirror," and the black ground which surrounds the mirror is termed 

 the " ground-area." 



t We know of no other lepidopterist who has observed a 6th stadium in the 

 larva <>l this species. The 5th stadium is by all considered to be the last. 

 Weismann's experience must have been quite unusual. 



