44 BRITISH LEPIDOtTERA. 



acts as the stimulus, and this view has been materially strengthened 

 by his experiments on larvae, such as Rumia luteolata, etc., which show 

 so much initial variation in nature, that some are green and some 

 brown. His observations on larvae of this species, as well as on those of 

 Ennouws quercinaria (anyularia), Selenia lunaria, Crocallis elinyuaria, 

 Pkiyalia pedaria, and, above all, Amphidasys betularia, show conclu- 

 sively that the colour of some larvae is much affected by the surround- 

 ing environment, and hence, as a general conclusion, we must assume, 

 as far as our knowledge at present goes, that the general green colour of 

 those larvae which essentially live among green leaves, is due rather to 

 the influence of the particular environment surrounding them than 

 to any direct action of the chlorophyll, which is consumed with their 

 food. Commenting on these experiments, Poulton says : " Of the 

 colour changes we must distinguish two main kinds : (a) Changes in 

 the colour of the true animal pigments, leading to various shades of 

 brown, grey, etc. (6) The change to a green colour modified from 

 plant pigment, in the food. When such a change of colour is possible, 

 the true pigments are always superficial to the green, and cannot be 

 retained without concealing the latter, the degree of concealment 

 depending on the amount and distribution of pigment. Thus, in 

 Amphidasys betularia, the true pigments are chiefly placed in the 

 epidermic cells, the green in the subjacent fat, whilst in many others, 

 the former are in the superficial layer of the cuticle, the latter in the 

 blood, or sometimes in the lower layers of the cuticle. But the appear- 

 ance of the green is not merely the removal of a screen, although this 

 must occur ; in some cases, at any rate, it also means the formation of 

 the green colouring matter itself." 



Probably the first attempt at ornamentation in the lepidopterous 

 larva consisted of longitudinal lines. These usually consist of (1) The 

 dorsal or medio-dorsal line (a line running down the centre of the 

 dorsurn, throughout its whole length). (2) Sub-dorsal lines (one on 

 either side of the medio-dorsal line). (8) Supra-spiracular lines (one 

 on either side: above the spiracles). (4) Sub-spiracular lines (one on 

 either side below the spiracles). Sometimes there is a spiracular line 

 running along and including the spiracles. The medio-dorsal line (as 

 such) is probably, occasionally, due to the alimentary canal showing 

 through the skin. It is certainly so in many transparent-skinned larvae 

 (Ephestia kukniella, etc.), and it is just possible that, whatever form its 

 modifications may now take, it originated in this manner. Weismann 

 has concluded, from his studies of the Sphingids, that the sub-dorsal line 

 arose before the spiracular, and Packard f shows how, after the sub-dorsal 

 and spiracular lines are formed, others are rapidly introduced and 

 some may as rapidly vanish, as necessary features of certain stages 

 which, when they become useless, are discarded. 



Weismann, in his Studies in the Tlwory of Descent, has shown that 

 the primitive markings of caterpillars were lines and longitudinal bands. 

 He further shows that larval spots are formed by interruptions, " the 

 serial atrophy," of the lines or bands. Packard says : The lines, bars, 

 stripes, spots, and other colorational markings of caterpillars, by which 

 they mimic the colours and shadows of leaves, stems, etc., have 

 evidently been, in the first place, induced by the nature of the food 



* Tram. Ent. Hoc. Loud., 1892, pp. 458*459. Boinbycine Moths of America, p. 15. 



