278 Mr. E. B. Poulton. Essential Nature of the [Apr. 23, 



In some cases there are indications of quite new markings in the 

 changes preceding pnpation. Thus in the larva of G. Libatrix black 

 patches appear on the sides of two (I believe) of the anterior seg- 

 ments, while green patches appear on corresponding parts of the 

 larva of Selenia Illunaria. 



6. The Causes of Colour in Pupce. 



In the pupas of nearly all Heterocera (except the few that are pro- 

 tectively coloured like the larvae, e.g., HJphyridce, JE. Angularia, &c), 

 the larval colours have entirely disappeared from the surface, and are 

 replaced by the darkened opaque cuticle of the pupa. The derived 

 pigments are, however, generally retained in the blood. Before the 

 covering has darkened, immediately after the last ecdysis, the pupa 

 possesses a colour partly due to its blood (when coloured), and partly 

 to its fat body. The effect of the former is seen in the parts where 

 the latter is absent, especially in the wings, legs, and antennae. These 

 parts are therefore green or yellow in the pupae of which the blood is 

 coloured by derived pigments. The rest of the body is white, and 

 through the transparent cuticle the lobulated fat body can be dis- 

 tinctly seen. These appearances can only be witnessed for a very short 

 time, since the semi-fluid surface rapidly darkens into the normal 

 reddish-brown or black ; although it is not uncommon for the colour 

 of the blood to be seen through the cuticle of the wings — the most 

 transparent part. There are, however, instances in which some of the 

 true larval markings can be traced upon the pupa directly after emer- 

 gence from the larval skin. Thus in S. Ligustri the oblique stripes 

 are distinctly seen upon their respective segments. In a specimen 

 placed in spirit before the appearances were obscured, the oblique stripes 

 have darkened into brown, while the surrounding surface remains 

 comparatively pale. This subject will repay future investigation, and, 

 I think it is probable that larval markings will prove to be commonly 

 present upon the pupae, if examined sufficiently early. When the 

 pupae of Heterocera are freely exposed, the constitution of their pro- 

 tective colouring is similar to that of the larvae. Thus in the dimorphic 

 (green or brown) species of Ephyra la.rva, the colour of the pupa 

 follows that of the larva. The green is due to chlorophyll in the 

 blood, and the colour is especially deep over the wings and adjacent 

 surfaces. The depth of colour is produced in certain positions by 

 reflection from a white surface of fat behind a layer of green blood, 

 the light having thus traversed the fluid twice ; while in other positions 

 the pupa is transparent. There are also black markings in the 

 Ephyra pupa, which are due to cuticular pigment, and therefore 

 remain in the empty pupa case. 



The pupa of A. Grossulariata is believed to be gaudily coloured 



