194 ME. E. B. POULTON ON THE EXTERNAL 



linustri * (see woodcut 2, natural size, showing the posterior part of an undarkened male 

 pupa from the left side). The purple borders of the strij)es are seen to bear a relation 

 to the segments similar to that borne during the larval stage. This is especially well 

 seen in the border of the last stripe. In the larva the last white stripe crosses the 

 seventh abdominal and enters the base of the caudal horn on the eighth ; its border is, 

 of course, just in front of it during this course. The border in the pupa crosses the 

 same segment, and its long axis points towards the anterior part of the scar of the 

 caudal horn (see woodcut 2, sc). So also the relation of the coloured borders to the 

 spiracles is just the same as that of the larva. The borders in tlie figure are more distinct 

 than in the spirit-specimen from which it was drawn, because the surface of the latter 

 has darkened to some extent upon the back, and the borders appear to be merely lines of 

 especial darkening as compared with the adjacent surface, which they resemble in colour 

 (brown). In another spirit-specimen of Sphinx Ugnstri (preserved for nearly two years) 

 the strijoes remain very distinct and still retain a purplish tint. On removing a portion 

 of the cuticle and examining its under surface, it was at once seen that the colour of the 

 borders is due to pigment in the adherent hypodermis cells, whicli can be detached with 

 loss of the colour. It is thus certain that the constitution of the coloured stripes in the 

 pupa is similar to that in the larva, while the dark surface of the former is entirely 

 different and due to a darkening of the cuticle. 



Similar facts are true of the pupa of Acherontia atropos. When examined immediately 

 after pupation the purple stripes and small circular patches (which probably spread from 

 the bases of shagreen dots) of the larva are distinctly seen through the undarkened pupal 

 cuticle. I have also observed the light oblique stripes, with their dark green borders, of 

 Smerinthus popuU and of S. ocellatvs, conspicuously appearing upon the surface just 

 after pupation. 



The importance of these observations in homologizing the larval and pujial segments 

 and structures is well shown by the following example : — ■" In the green freshly exposed 

 pupa of Aglia tau all the markings of the larva are very distinct, and the subspiracular 

 line which forms so prominent a feature of the larva, and which is continued along each 

 side of the anal flap to its extreme apex, is equally conspicuous in the pupa, and occupies 

 an identical position in relation to the terminal anal spine, which in this species is blunt 

 and covered with an immense number of irregular hook-like cuticular processes " f (see 

 Plate XXI. fig. 16 for the general form of this part of the pupa). Hence the j)osition of 

 the marking affords valuable confirmation of the identification of the anal flap of the 

 larva with the terminal spine of tlie pupa, to be further discussed below. 



There is little doul)t that the careful examination of freshly formed pupae will prove 

 that such markings are of very general occurrence. 



* See Proo. Roy. Soc. vol. xxxviii. p. 278, ia which this example is briefly described, 

 t Poulton, in Trans. Eut. Soc. Lend. 1888, p. 560. 



