the colours of certain Lepidoptera. 



351 



C. Dark and Green Surroundings in Dim Light. 



(See Table, page 350.) 

 These experiments were conducted with the object of 

 investigating the relation between the habits of the larvfe 

 as regards resting and feeding, and the external con- 

 ditions as regards light. In this respect I did not come to a 

 conclusion ; but the experiments haveproved very valuable 

 in another way, — in testing the effect of dim light upon 

 the colour-relation between larva and their surroundings. 

 The effect is very clear, and conclusively proves that 

 light is the agency which influences the larvae. For, with 

 this dim illumination, neither green nor (probably) even 

 dark surroundings produce their full effect, the influence 

 of the former naturally being diminished fnr more than 

 that of the latter. Thus green surroundings continued, 

 in this case, for the whole of larval life (XXI. and XXIII.) 

 failed to produce a single green larva, only 2 out of 33 

 being greenish intermediate. It must be remembered, 

 however, that XXI. was much crowded, as were the 

 larvffi of XXIII. previous to July 16. On the other hand, 

 the dark twigs in XIX. and XXII. produced very different 

 effects from those of I., where, however, they were added 

 7 days earlier. Although the effects are diminished, they 

 are not altogether absent even in the case of the green 

 surroundings, for we find that the larva) exposed to the 

 latter (XXI. and XXIII.) are the lightest, those exposed 

 to dark twigs (XIX. and XXII.) are the darkest, and 

 those exposed to the stems of dock which became dark 

 brownish (XX.) are intermediate. When we compare 

 these results with those of the next experiments, in 

 which dark and green surroundings in darkness produced 

 the same effect on the larvae, it becomes clear that 

 light is the agency by which the colour-changes are 

 directly, or more probably indirectly, brought about. 



D. Dark and Greem Surroundings in Darkness. 



Experiments XXIV. and XXV. 



XXIV. 



Lamp-shaile. Height, 132 mm. ; 



approximate capacity, SCO cc. 



Kept in same illumination as XIX. 

 — XXIII. from hatching until July 

 9. From July 9 to Aug. 3 kept in 

 total darkness, except when fed and 

 when XIX. — XXIII. were being 

 shifted from light to darkness, and 

 vice I'cr.srt, every 24 hours. Green 

 surroundings as in XXIII. , &c. 



Julij 9. — 25 larvae arranged in 



is cylinder. 



XXV. 



Lamp-shade. Height, 129-5 mm. 

 approxiviate capacity, 750 cc. 



As in XXIV., except that abun- 

 dant dark twigs were added July 16. 



Jiilii 9. — 25 larvse introduced, aa 

 in XXIV. 



