320 Mr. I'oulton's further notes niion the 



changes of colour before pupation, and this theory is, I 

 think, much supported by the unusual change of colour 

 in the larva of E. angularia. 



15. On a curious habit observed in some larvae 

 BEFORE pupation. — This summer (1884) I have been 

 told by my sister of a curious habit that she has noticed 

 in the full-fed larvae of M. stellatarum. When these 

 have ceased to feed, but before the colour has darkened, 

 they cover themselves all over with a brown fluid from 

 their mouths. My sister describes the process as 

 occupying considerable time, being conducted with the 

 greatest care. The mouth is even brought into contact 

 with the dorsal surface of the 1st thoracic segment, so 

 that this is moistened together with all other parts of 

 the larva. The same observer considers that several 

 layers of fluid are poured out over the larva, and she 

 believes that the changes of colour before pupation are 

 produced in this way, stating that the moistened part of 

 the surface is quite different in colour from that which 

 has been hitherto untouched. This interesting observa- 

 tion seemed to render intelligible a fact which must have 

 been noticed by every breeder of caterpillars, i. e., that 

 adult larvae which are thoroughly wet all over the body 

 are often seen in the breeding-cages. I had also noticed 

 that such larvae had ceased to feed before this took 

 place, and that soon afterwards they changed colour and 

 wandered about 'to find a spot suitable for pupation. 

 With this interpretation I watched carefully, and in a 

 few days I saw the adult larva of S. populi carefully and 

 very systematically covering itself with fluid. I then 

 recognised the moistened surface as quite similar to that 

 which I had often seen before, when I did not know of 

 the method by which the moisture was applied. Since 

 then I have seen the same thing in M. stellatarum, 

 although in this case the fluid (if any) seemed to dry at 

 once, and was hardly ever visible. The movements of 

 the head are exactly those indicated by the term 

 " licking." It seems likely that this habit is really very 

 common, perhaps universal, among larva?, but 1 do not 

 feel any certainty as to its use. I do not see how it can 

 affect the change of colour, for this must be due to com- 

 paratively deep-seated processes, whereas the fluid is 

 superficial. Further, the larva of S. jwjyiiU does not 

 change in colour to any extent, and only on the back, 



