86 BRITISH LEPIDOPTEEA. 



terous larvffl was due to green pigments dissolved in the blood, whilst, 

 in the case of certain Sphingid larvae, he believed that the pigments 

 passed from the blood into the hypodermic cells, and so coloured the 

 larvae, whilst later experiments (2'rans. Ent. Soc. Lond., 1886, p. 169) 

 led him to suppose that the colour of the larva of S. ocellatm was 

 essentially due to the segregation of the pigment in these cells, the 

 blood itself being comparatively free- from the pigmentary matter. He 

 further states that before pupation the pigments are withdrawn from 

 the cells, and are dissolved in the pupal blood. Poulton concludes 

 that the larva of S. ocellatus maintains a colour-relation with the food- 

 plant on which it is hatched, adjustable within the limits of a single 

 life, and that the predominant colour of the food-plant itself is the 

 stimulus which calls up a corresponding larval colour, and, further, 

 that natural selection has finally produced a resemblance either 

 general or special to something which is common to all the food-plants 

 of the larva, or to some one or more of them, the larva being less 

 protected upon the remainder ; but, in this case, the same gradual 

 process has finally given the larva a power which (relatively) imme- 

 diate in its action, enables the organism itself to answer with corre- 

 sponding colours the differences which obtain between its various food- 

 plants (Proc. Eon. Soc. Lond., 1886, p. 172). 



A larva of Cossus lir/nipo-da, exhibited at a meeting of the Ent. 

 Soc. of London, some years ago, had lost its ordinary colour, and 

 had become pink, and then white, from having been deprived 

 of its natural food, and confined for eighteen months to a diet of pink 

 paper, with which the cardboard box in which it was kept was lined, and, 

 subsequently, to the cardboard itself. It was suggested that food assimi- 

 lated in a more or less unaltered condition, had probably influenced the 

 colour of this particular larva. At the same time, the later (white) 

 coloration may have been due to an etiolated appearance caused by 

 starvation. It appears certain that in nature this mode of assimila- 

 tion of food must be considered as the basis of any direct influence that 

 may be exerted by the coloration of the food on the coloration of the 

 larva, and this is borne out by the yellow coloration of larvae of certain 

 Eupithecia species (absynthiata, etc.), found feeding upon ragwort flowers, 

 and similar instances. As a rule, however, the colouring matter of 

 flowers and leaves cannot be so directly used, and only some modifica- 

 tion of the colouring matter at the most, can, in very many instances, be 

 elaborated into the colouring matter of the larva, for the physiological 

 processes demand the digestion, as well as the assimilation, of all 

 material that enters the larval blood, and one would surmise that it is 

 only after entering the blood that it can be elaborated into new colouring 

 pigments by the larva. That it is usually not a mere matter of the 

 transference of plant pigment to the larva is certain. It is probable 

 that in such dimorphic larvae as those presented by species like 

 Hadena oleracca, Mamestra persicariae, Geometra papilionaria, and 

 others, in which two forms appear on the same plant under identical 

 conditions, the difference is essentially a difference of epidermal struc- 

 ture, the green colouring pigment being in the subjacent fat cells (or 

 rather in the blood bathing these cells), in each form of these species, 

 but screened off, as it were, in the darker forms, by a modification of 

 the integument itself. Such appear to be the more prominent facts and 

 suggestions relating to phytophagic coloration. 



