USE OF LARVAL APOSEME BY PUPA 217 



opposite to the posterior extremity of the occupant, a 

 weak spot, ahiiost a hole, is left. When the caterpillar 

 becomes a chrysalis the discarded brightly coloured larval 

 skin is pushed out so that it partly projects through this 

 hole. It is naturally to be expected that the adult moth 

 would emerge through this hole, but it does not ; it pushes 

 its way out in the usual manner through the other end of 

 the cocoon. Now if the object of the weak spot is to 

 allow the discarded larval skin to be extruded so as not 

 to take up space inside the cocoon, one would expect 

 it to be got rid of completely, but this is not the case ; 

 it remains partly inside, partly outside, ^ its bright colours 

 freely visible. Apparently the pupa makes use of the 

 discarded aposematic skin to protect itself. I have not 

 met with another case of this partial extrusion of the 

 larval skin through an orifice especially provided. 



Insects furnished with well marked aposemes are 

 commonly said to be protected by the possession of sting, 

 distastefulness, spines, hairs, irritant fluid, exceptional 

 hardness, etc. It must be understood that this immunity 

 from attacks by birds or mammals is not by any means 

 claimed to be absolute at all times, but is entirely relative, 

 depending upon the abundance of insect food generally, 

 of that species in particular, and the state of hunger of 

 the enemy, who, when food is difficult to obtain, will eat 

 species which he would pass by when more edible insects 

 could be easily found. ^ Also it must be remembered that 

 certain creatures appear to be specialized for devouring 

 prey which others pass over. 



^ In a certain nnmber of cases the skin is completely extruded — 

 evidently the habit, if it is of protective value, has not yet been carried 

 to its fullest efficacy. 



2 See Poulton, E. B., The Colours cj Animals, pp. 180, 181. Marshall, 

 G. A. K., The Bionomics of South African Insects. Trans. Ent. Soc. 

 Lond., 1902, part iii. Swynnerton, C. F. M., Proc. Ent. Soc. Land., 

 February 3, 1915; and in "Experiments and Observations bearing on 

 the Explanation of Form and Coloviring." Journal Linn. Soc, 1919» 

 Zoology, xxxiii. 



