134 PHYSIOLOGY OF THE INVERTEBRATA. 



very similar process to the darkening of cuticular pigment 

 on larvfe, and the darkening of the pupal covering. It has 

 always been assumed that this darkening is due to light, 

 but 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, Poulton 

 has never observed that darkness made the least difference to 

 the darkening of pupa?. It is, therefore, " very probable that 

 this will also prove to be due to oxidation, and jDOSsibly to 

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

 blood." 



Poulton has observed that " the brown and colourless 

 blood darkens as well as the green." 



The Action of Reagents. — The action of {<i') alcohol (fifty per 

 cent.) on the blood of P. Bnceiihalvs was to precipitate 

 proteids ; and if the mixture is shaken, " the proteids and 

 pigments are precipitated as yellowish-green clouds, and in a 

 few minutes the upper part of the liquid becomes blue, and 

 ultimately black, from the formation of coagulum. The 

 proteids are decolourised and sink, the alcohol remaining 

 yellow with xanthophyll (the chlorophyll disappearing). 

 Absolute alcohol does not lie on tlie top of the blood (like 

 diluted alcohol), but mixes with it at once. (h) Chloroform 

 benaves in the same manner as ether, but it dissolves nothing 

 coloured from the green coagulum ; the latter contracts in a 

 few hours, and a clear blue liquid appears between it and the 

 sides of the tube. The exposed surface of the coagulum 

 (the chloroform having sunk to the bottom) rapidly becomes 

 black, (c) Distilled water, like weak spirit, lies on the top of 

 the blood with a cloud of precipitated proteid (probably 

 globulin) above the junction. On shaking, the cloud disap- 

 pears, and the blood only seems diluted ; if now more water 

 be added (altogether many times the volume of the blood), in 

 a few minutes the whole fluid becomes cloudy, remaining 

 dark -greenish. On filtering, a blue solution comes through, 

 which slightly darkens for some hours. With less water the 



