1885.] 



Colouring of Phytophagous Larvae, 



295 



on the surface, while the blood beneath became translucent in- 

 stead of clear and transparent. On removing the crust a second 

 thin one was formed, but on removing this no further coagulation 

 took place. If in sealing up blood, or placing it in a tube section, 

 a bubble of air is accidentally included, coagulation takes place round 

 the bubble, but not elsewhere. This black substance is the normal 

 clot, for the injured places on larvae which have healed are always 

 black, notably the horns of Sphinx larvae which have been nibbled off 

 by others of the same species. The coagulation takes place after the 

 addition of water, or of a saturated solution of neutral salt (sodium 

 sulphate). The occurrence of a reducing agent in the blood appears 

 to be very remarkable, but it is possible that the substance is capable 

 of again yielding up its oxygen, and so acting as a carrier. I have 

 observed that if fresh blood be added to that which is turning black 

 on the surface, the black clouds are redissolved. If this be not so, it 

 is difficult to see how the blood can be the internal medium for the 

 supply of oxygen in these animals, and one is tempted to the supposi- 

 tion that in the tracheal system we have a means for the supply of 

 oxygen direct to the tissues. I hope to investigate the question this 

 summer. Another suggestion which occurred to me was that the 

 coagulation is a very similar process to the darkening of cuticular 

 pigment on larvae and the darkening of the pupal covering. It has 

 always been assumed that this darkening is due to light, bnt it takes 

 place rapidly and completely in pupae buried several inches under 

 ground, in compact and opaque cocoons, or sometimes in the heart of 

 a tree. Furthermore, I have never observed that any attainable dark- 

 ness made the least difference to the darkening of pupae. I therefore 

 think it very probable that this will also prove to be due to oxidation, 

 and possibly to the formation of a substance similar to the black clot 

 of the blood. 



The brown and colourless blood darkens as well as the green, but 

 the latter seemed to yield the most marked results, although I have 

 not observed a sufficient number of instances, except in the case of 

 the green blood, to be able to draw conclusions. There is great 

 variability in the time that elapses before coagulation, and I have 

 seen samples that have not clotted at all. From my memory of the 

 blood of 8. Ocellatus in the larval state, I believe that the blood 

 coagulates far more rapidly than that of the pupa. 



Action of reagents. — The effects of ether and absolute alcohol have 

 been already described. The blood experimented upon was that of 

 P. Bucephalus. 



Fifty per cent, spirit, if poured carefully, lies on the top of the 

 blood, and there are white clouds of precipitated proteids just above 

 the junction. If shaken, the proteids and pigments are precipitated 

 as yellowish-green clouds, and in a few minutes the upper part of 



VOL. XXXVIII. Y 



