302 Mr. Poulton's notes in 1886 



Thus in many larvae the swollen lateral area of both 

 segments is seen to have undergone a marked alteration 

 in colour. Sometimes the pigment in the larval hypo- 

 dermis disappears, and the areas are coloured by the 

 green blood of the insect (e. g., Selenia illunaria, and in 

 many other larvae) ; but in other cases new pigment may 

 be deposited in the larval cuticle, and an entirely new 

 marking may thus make its appearance at the extreme 

 end of the larval life. The most striking instance which 

 has come under my observation is afforded by the bright 

 green larva of Gonoptera libatrix, in which the convexity 

 of each thoracic swelling becomes covered with a black 

 patch, that upon the mesothorax being the larger and 

 of a deeper tint. The appearance of the anterior part 

 of the larva just before pupation is shown in Plate X., 

 fig. 11 (X 2). Thin sections examined under a high 

 power reveal the fact that the pigment is placed in the 

 superficial layer of the cuticle, thus occupying the 

 position in which black colouring-matter apparently 

 always occurs. This formation of pigment at such a 

 time, and in such a position, is of great physiological 

 interest, for either the pigment itself or its factors must 

 have traversed the lower thicker lamellated layer of the 

 cuticle in order to reach the thin superficial layer, thus 

 clearly showing that no part of the cuticle is beyond the 

 reach of physiological processes while it forms the 

 covering of the living larva. If there were a time in 

 which the larval cuticle could be looked upon as a mere 

 mechanical investment it would be at this very period, 

 when it is to be shortly cast off, and when the larval 

 hypodermis cells are elaborating, or are just about to 

 elaborate, a new (pupal) cuticle beneath the surface. 

 But at this very time we have the clearest indications 

 that the larva has not lost its organic hold upon its 

 superficial investment. It would be of great interest to 

 carefully investigate the exact time at which the pigment 

 appears, and to examine by means of sections its 

 relation to the first formation of the pupal cuticle. It 

 is impossible at present to form an opinion as to 

 whether the appearance is of any significance in relation 

 to the difficult question of the origin of wings, or 

 whether (as appears more probable) it is merely an 

 incidental result which attends the commencement of 

 new activities by the hypodermis cells. In Plate X., 



