METAMORPHOSIS IN LEPIDOPTERA. 29 



Many incidental phenomena connected with the pupal moult have 

 been observed. One of the most curious was described (Trans. Ent. 

 Soe. Lond., 1887, p. 302) by Poulton and further elaborated (Ent. 

 Record, x., p. 116) by Chapman. It consists of the development of 

 black pigment over the wing areas in the larva of Scoliopteryx libatrix 

 as soon as it commences to spin its cocoon and some time before it 

 actually moults. These two black patches are very conspicuous on the 

 green larva, the colour being entirely in the superficial layer of the 

 larval skin and moulted with the latter. The pupa itself is sooty-black 

 and this blackness is due to the presence of a special pigment, and it 

 would appear that this larval pigment is similar to that of the pupa, 

 and is connected with it in some way. Chapman points out that the 

 material for this pigment is present in the superficial layer of the 

 chitinous covering of the pupa at moulting, whilst it is still green and 

 soft, and that the pigment is formed from it by some chemical change 

 on exposure to air and light, probably by oxidation. This material, 

 he considers, is probably formed from some constituents of the 

 epidermic cells that break down to liberate the effete superficial layer 

 from the dermis beneath, most of which is probably at once absorbed by 

 the new layer of epidermal cells forming on the surface of the dermis. He 

 then explains the formation of the black larval wing-patches as follows: — 

 " During the larval life the wing lies in an invaginated pocket of the 

 dermis, but at the date of the change to pupa it does not do so, but 

 lies immediately beneath the effete skin that is about to be thrown off, 

 and, therefore, one of the changes that occur at the end cf larval life, 

 is the disappearance of the double fold of dermis, between the epidermis 

 and the wing. When the outer layer of this frees itself from the 

 epidermis, it -no doubt does so by the same process as that which 

 develops pigmentary material elsewhere, but here the dermis below 

 has itself also to disappear, so that this material is not at once 

 appropriated by the proper new cells beneath, and there is a certain 

 excess of it, so to speak, free. This then permeates the effete cuticle, 

 reaches the surface, and undergoes the oxidation, or other process, that 

 converts it into pigment. There is no other portion of the larva where 

 pigmentary material might thus be set free, but, in this situation, it is 

 difficult to see how it could be avoided without a different physio- 

 logical process having been evolved for this little area. If we knew 

 the precise time at which the wing became disencapsuled, we could 

 better judge as to the probability of this being the correct hypothesis. 

 It would also throw light on the subject to know if other instances of 

 the same coloration of the larva were confined to cases in which the pupa 

 has pigmental colouring, and that it does not occur where the ordinary 

 chitinous brown only is the pupal colouring." One would be interested 

 to learn whether the blackness of the "Osborne membrane " of Anosia 

 archippiiH, mentioned by Edwards (Canadian Entomologist, ix., p. 231), 

 has been developed in a similar manner. 



It sometimes happens before the last larval skin is exuviated that 

 one can see, through the transparent skin of certain larvae, some 

 portions of the pupa which have already assumed a brown chitinous 

 colour, and, in many pupae, immediately after the moult, there are 

 portions already brownish, whilst the greater part of the pupa is green 

 and soft. Chapman writes (Ent. Record, x., pp. 117-118) of this as 

 follows : "In Scoliopteryx libatrix, before the moult, a slight ruddy tint 



