208 Mr. W. Bateson on Variation in the 



{e). On opening a larva, whether young or nearly full- 

 fed, the contents of the alimentary canal are hright 

 green, but upon exposure to the air they turn to the 

 red-brown colour of the evacuations seen in the breeding- 

 cages. By washing out the contents of the alimentary 

 canal, and filtering out the debris of food, a clear green 

 filtrate was produced, which turned red-brown in the 

 course of some minutes. There can be no doubt that 

 this change is connected with oxidation, for it takes 

 place more rapidly if the test-tube containing the fluid is 

 shaken, and immediately if yellow nitric acid is added. 

 Moreover, if the contents of the alimentary canal are 

 placed on a glass plate, the surface soon turns in colour, 

 while the lower part next the plate may be seen to be 

 still green. The change from green to red therefore 

 results from oxidation. 



The actual origin of this colouring matter in the 

 alimentary canal is not easy to determine. There are 

 two chief possibilities ; first, that the green colour is a 

 substance (such as bile, for example) secreted by the 

 animal ; or, secondly, that it is formed from the food. 

 The first of these is almost certainly disproved by the 

 fact that there is no green substance in the walls of the 

 gut, or in the tissue adjacent to it, which undergoes the 

 change described ; whereas, if the substance were the 

 result of secretion, it would be expected that this would 

 be the case. Filling the tissue-spaces surrounding the 

 gut there is indeed a green fluid, but this retains its 

 colour on exposure unchanged, not even turning to 

 black, as do the body-cavity fluids of so many larva3. 



If, then, the colouring substance is not a secreted 

 body, but is formed in some way by digestion from the 

 food, the question naturally suggests itself, is it a 

 chlorophyll product ? That this is so is on the whole 

 likely, but I know no way by which it might be proved 

 to be so. For since the whole gut is filled with chewed 

 leaves, there is of necessity much chlorophyll present, 

 and it is not possible to obtain the colouring substance 

 free from chlorophyll. 



In this connexion it should be remembered that the 

 brown colour of the cocoons is a very good match with 

 the brown to which hawthorn leaves turn in winter, 

 and it is not unlikely that the change from green to 

 brown undergone by the colouring substance of the 



