1887.] VALUE OF COLOUR AND MARKINGS IN INSECTS. 2G3 



its imitative resemblance complete by entire quiescence, and it is 

 usually effectually protected in other ways ; but the larva innst feed, 

 and at tiie same time is sluggish in its movements, defenceless, and 

 when palatable is more relished than any other stage, for it does not 

 possess the hard investment of the one or the scaly covering of the 

 other. It has also been seen that an unjjleasant taste may arise 

 incidentally at this period. Assuming, then, that the great needs 

 of certain larvae have been met in this way, there will be the 

 tendency for the unpleasant quality to pass on by sirnjile continuity 

 into the other stages; and if these are hard pressed, there is always 

 the possibility that such attributes may be made the starting-point 

 of a similar method of defence for them also. Hence 1 believe we 

 shall nearly always find that conspicuous unpalatable imagos develop 

 from larvae which are also unpalatable and conspicuous, and such a 

 conclusion is entirely borne out by the table. But the unpleasant 

 quiility may pass on in the same way into other stages, which hold 

 their own successfully by elaborate and perfect j)rotective resemblances, 

 and then there will be no tendency for the quality to be made use 

 of, although it will always remain as a possibility should the 

 species be worsted by its enemies in these stages. It must be 

 remembered that the possession of an unpleasant taste by a 

 protectively coloured species can never be injurious in any way to 

 itself except in so far as it causes the destruction of a greater amount 

 of insect-life, inasmuch as the part contributed by the species itself 

 to the total destroyed does not count as food under ordinary circum- 

 stances. And the species itself remaining on the same protective 

 lines as tlie great mass of palatable species, it will itself come in for a 

 proportional share of the extra loss which ft)llows from the fact that 

 it is not relished as food. But so long as these unpalatable species 

 remain in a small minority, the reaction of their own inedibility upon 

 themselves will be inappreciable. Mr. W, Esson has kindly expressed 

 the danger actually incurred in a mathematical form, showing that it 

 is inappreciable when the inedible species are relatively few. If 

 there were a practically unlimited number of protectively coloured 

 insects consisting of two sets of species, the one set edible and the 

 other inedible and consisting of individuals in the ratio of 100 : 1, it 

 is reasonable to suppose that in any number n of captures there will 

 be killed of each set a number of individuals proportional to the 

 numbers in the sets themselves ; i. e. of the edible ^^ and of the 

 inedible ~. The insect-eaters will go on catching the insects until 



the edible -^ becomes equal to the number required for their food — 

 a. Therefore -j^ = a and n = -jq^; therefore there are caught of 

 the inedible species ~) that is ^. 



Considering the above-mentioned exceptions among the imagos 

 rather more in detail, it would certainly be difficult to find any species 

 with an appearance more completely the opposite of that produced 

 by the typical warning coloration than the imagos of P. hurephala 

 and O. antiqua. The special character of the imitative resemblance 



