170 Mr. Poulton's notes in 1885 upo7i 



that artificial digestion could be successfully performed 

 than in tlie case of higher animals. Nevertheless, there 

 are certain ways in which the problem could be attacked 

 with every prospect of success. (1). There are many 

 larvas which eject a green fluid from the mouth, and this 

 fluid has the same spectrum as that of the blood (in the 

 instance examined). It is probable that such a solution 

 might be made by artificial digestion. (2). The blood 

 of some large larva in which the pigments passed into 

 the hypodermis cells might be investigated at various 

 times after a meal and after fasting, and in this way we 

 might expect to trace corresponding fluctuations in the 

 amount of pigment in the blood, as proved by the 

 spectroscopic examination of equal thicknesses. (3). In 

 the same way the pigments might be examined in newly- 

 hatched larvae, before and also at various times after 

 their first meal, when more extreme fluctuations might 

 be witnessed. 



I hope to pursue such a line of investigation during 

 the present summer, and also to attempt the artificial 

 digestion of plant-pigments. 



15. On the considerable loss of weight in the pupa 



immediately after throwing off the larval skin. 1 



have previously suggested that the rapid darkening of 

 the pupal integument, freshly exposed after throwing off 

 the larval skin, may be partially due to oxidation (Proc. 

 Eoy. Soc, No. 237, 1885, p. 295). Believing this to be 

 the case, I determined to weigh some pupae immediately 

 after the change, thinking it possible that there might 

 be some gain in weight due to the absorbed oxygen. To 

 my astonishment I found that there was an immense 

 loss in weight during the darkening. This does not, 

 however, disprove the oxidation, for the loss is mainly 

 due to evaporation, and it is therefore clear that the 

 giving off of water is one important factor in the 

 liardcning and darkening of the fluid surface of the 

 pupa. Thus, if the evaporation be checked, the pupa 

 does not darken. I have placed a green undarkened 

 pupa of Gonoptera libatrix in a beaker of water, and 

 have exposed it to the rays of the sun for some hours, 

 and the pupa did not darken in the least. On removing 

 it from the water the pu})a recovered and rapidly 

 darkened. Again, I have passed up the green pupa of 

 SinerititJius jx'puli through water in a tube into a small 



