the colours of certain Lepidopterit. 37 1 



to be amply supported by the last table. In order to 

 test this conclusion more fully, I have constructed 

 another table, in which the lengths of the periods and 

 stages are shown in the pupfe of the various degrees of 

 colour, without taking into account the conditions to 

 which they had been subjected, except as regards the 

 presence or absence of food. 



{See Table 1 a, x>age 370.) 



This table shows a remarkable uniformity in the 

 length of Stage III. in pupae of all degrees of colour, 

 just as the preceding table showed it in all conditions of 

 illumination, &c. On the other hand. Stages I. and II., 

 upon the whole, exhibit a marked tendency to become 

 longer as the pupse become darker. There are exceptions, 

 but the general tendency is clear, and especially so in 

 the case of larvae with food. Besides, the history of the 

 exceptions lends no support to the theory that the pro- 

 traction is determined by darkness, apart from any 

 influence on the pupal colours. The table suffers from the 

 small numbers employed in taking the averages. The 

 careful study of these observations, made in 1887, con- 

 vinces me that I was mistaken in maintaining, as the 

 result of a far more superficial examination of the figures, 

 that " there did not appear to be any evidence for the 

 supposition that the gilded pupae pass through a sborter 

 preparatory period than those which are less brilliant, 

 when both are equally exposed to light" (Note added 

 Sept. 10th, 1887, to p. 339 of Phil. Trans., 1887, B.). 



I believe, on the other hand, that we are warranted in 

 the conclusion that dark surroundings tend to prolonfj 

 Stages I. and II. {taken together) of the preparatory 

 period, and that this protraction is associated with the 

 production of the colourless precursor of the dark super- 

 ficicd pigment. 



I have hitherto treated Stages I. and II. together, but, 

 if the above conclusion be valid, it is clear that Stage II. 

 is alone concerned ; for in the earlier wandering stage 

 the larva has not yet reached the surface by which it is 

 to be affected, and, as soon as it reaches it. Stage 11. 

 begins. 



The question as to whether darkness acts, except by 

 promoting the formation of dark pupae, was most easily 

 answered by observing whether dark surfaces in strong 



