1885.J Colouring of Phytophagous Larvce. 311 



distance, and in fact there are examples of 8. Ginera and 8. Baby- 

 lonica in the garden itself. 



It seems therefore that the explanation offered above must be 

 correct, and if so we have an instance of a character (larval coloura- 

 tion) that is shown in a very obvious manner to be the result of the 

 interaction between the influences at work in an individual life and 

 the inherited tendencies following from the influences that moulded 

 the lives of ancestors. In this case, too, there is a fairly accurate 

 test for the predominance of either element, in observing the 

 resultant tint, and making allowance for the tendencies (already 

 gauged) of the food-plant. 



The case of 8. Ligustri is also to be explained in a similar way, 

 for here, too, we have the difficulty of conflicting experience 

 (Mr. Davis' and my own). I have a considerable number of pupae 

 of 8. Ocellatus, with careful notes of the colours and food-plants of 

 their respective larvae, so that I hope to be able to test the above 

 theory very conclusively in the summer. 



21. The Essential Nature of the Changes in Colour Produced by Food- 

 plants. 



It is first necessary to carefully describe the appearance of the 

 varieties of 8. Ocellatus, before explaining the underlying cause of 

 the colour, by reference to larval or derived pigment. 



The larva of 8. Ocellatus is covered with minute white points 

 (which are the tubercles at the bases of rudimentary hairs), con- 

 ferring upon the skin a shagreened texture. The colour is much 

 modified by these dots; and their arrangement, together with the 

 spreading of white areas from their bases, and the coalescence of 

 such areas, form nearly all the markings of the larva. The dots are 

 very variably developed; at one time I thought that the whitish 

 varieties must be caused by their relative predominance, obscuring 

 and modifying the green ground-colour. Careful observation, how- 

 ever, convinced me that the difference is not due to this. The most 

 extreme whitish varieties are almost white upon the back, above the 

 horizon of the old subdorsal line. Below this the bluish-green tint 

 predominates (the line of demarcation being very sharp), while the 

 under surface is dark bluish-green. Careful examination of the 

 white dorsal surface with a lens shows that the green is obscured 

 (and almost obliterated) by a comparatively superficial accumulation 

 of white masses, while the green when present seems to shine 

 through from a lower level. On the under surface there is nothing 

 to obstruct the effect of the green (since the shagreen dots are very 

 minute, and the white masses are absent). The lateral surfaces offer 

 intermediate effects produced by intermediate conditions. An 



VOL. XXXVIII. z 



