q/ certain lepidopterous larva and pupce. 47 



In the former case the white dorsal stripe (with its 

 narrow dark central line) was not distinguishable from 

 the edge of the leaf, except on a close inspection. The 

 effect of the dark shading on each side of the white 

 stripe was to produce an appearance of lateral com- 

 pression, so that the thickness of the larva did not 

 attract attention. The fine white spiracular line could 

 not be seen from above, and was only visible from the 

 side when it was carefully searched for. It seems to 

 take no part in protection. At first I thought that this 

 was merely an interesting case of protective marking, 

 but a little investigation led me to suspect that the nature 

 of the colouring was peculiar. 



The fine dark dorsal line was certainly the dorsal 

 vessel, and its pulsations were distinctly visible to the 

 naked eye. It formed a darker line than I have seen 

 (similarly caused) in other larvse, and evidently in this 

 case the skin was especially transparent. Carefully 

 examining the white stripe with a lens I found that it 

 had the peculiar lobed appearance of the fat body, and 

 that it was moved by the pulsations of the dorsal vessel. 

 Thus it was certain that the white stripe was also due to 

 some internal part of the larva shining through the 

 skin. Similarly, with the simple lens, I could distinctly 

 see the tracheae radiating from each spiracle, and I was 

 led to believe that the fine spiracular line was merely 

 due to the main longitudinal tracheal tube on each side. 

 Dissection entirely confirmed all these suspicions, and 

 showed that the only true coloration of the skin — caused 

 by a pigment deposited in its own cells — was the black 

 shading on each side of the white stripe. The general 

 green colour is chiefly due to the fluids of the body, the 

 contents of the digestive tract and the green colour of 

 many of the tissues, notably those cells in which the 

 deposition of fat is taking place. 



We have here a remarkable instance of protective 

 colouring due to internal organs. The case of the fat 

 body is especially interesting. Apparently the first cells 

 to become filled with fat globules, and to gain a white 

 appearance, are arranged in two rows, one on each side 

 of the dorsal vessel. But this process cannot be carried 

 on indefinitely, or the white band would become too wide 

 for protective purposes ; and the massing of mature 

 cells elsewhere would cause white colours to be seen 

 through the transparent skin, if the massing took place 



