lepidopterous larvce and jmpce. 169 



many species (especially Noctuee) was cine to the derived 

 green pigments dissolved in the blood. At the same 

 time it was argued that in other species (green Spldnijida, 

 &c.) the pigments passed from the blood into the hypo- 

 dermis cells, and so coloured the larvae. This latter 

 conclusion seemed certain, although it had not been 

 experimentally investigated, because I was working at 

 the subject at a time of year when I could only obtain 

 Noctua larvae. I was therefore uncertain whether the 

 colour of the blood assisted in producing any of the 

 ground colour in those larvae in which the colour was 

 also segregated in the hypodermis cells. During the 

 past year I investigated the subject in the larva of 

 S. ocellatus, and I found that the blood is only very 

 faintly tinged with derived pigments, and that it cannot 

 produce any effect upon the larval appearance until it 

 has been collected in the superficial cells. It is probable 

 that in such larva the modified plant-pigments are 

 slowly passing from the digestive tract to the hypodermis 

 cells through the medium of the blood, and that the 

 blood itself at no time contains a large quantity of 

 pigment. Before pupation the pigments are withdrawn 

 from the cells, and are dissolved in the (pupal) blood, 

 which therefore possesses a concentrated solution of all 

 the pigments that have passed through this medium 

 during the whole of larval life, except those which have 

 been destroyed (if any). Such conclusions render it 

 probable that the most complete demonstration of the 

 vegetal origin of the derived pigments will be a matter 

 of great difficulty, for the amount that passes through 

 the digestive tract as the result of any one meal must 

 be very small, and probably even less could be obtained 

 by carrying on artificial digestion outside the body of the 

 larva. And this is likely to be the case with the larvae 

 in which the blood itself retains all the pigments which 

 have passed through the walls of the digestive tract, for 

 in these larvae it is probable that only a minute quantity 

 passes through as the result of any one meal. Further- 

 more, the fact that the derived pigment is associated 

 with a proteid in the blood renders it almost certain 

 that the processes of modification and association are 

 the direct results of protoplasmic activity, and not the 

 results of ferments, &c., which have themselves been 

 formed by the latter agency. Hence it is far less likely 



TRANS. ENT. SOC. LOND. 188G. PART II. (jUNe). N 



