272 



Mr. E. B. Poulton. Essential Nature of the [Apr. 23, 



In the reports of the British Association at Southport (1883), 

 Dr. MacMnnn further states that on withdrawing the intestinal con- 

 tents, the green colour and band disappear (Krukenberg also states 

 that the band is due to the contents of the digestive tract, quoted in a 

 letter to " Nature " by Dr. MacMunn for the week ending January 10th, 

 1885). I have not yet examined the larva of P. Bapce from this point 

 of view, but I think it is very probable that the green colour is due to 

 the blood which may have been also lost when the contents of the 

 intestine were removed. I shall show later on that chlorophyll (or 

 some modification of it) passes through the digestive tract and tinges 

 the blood of Lepidopterous larvae, and that the colour of green larva? 

 is often due to this cause alone. I am sure that the contents of the 

 digestive tract cannot account for the ground colour of a larva (such as 

 this) , in which the green is at all bright and distinct. Furthermore, 

 the blood is extremely likely to be lost in any manipulation of a larva, 

 for it exists under pressure and exudes from a very small aperture. 

 If the intestine was dissected out, there can be doubt of the loss of the 

 blood. 



Dr. MacMunn also alludes to the discovery of chlorophyll in the 

 elytra of cautharides, and states that he has confirmed this observa- 

 tion. He believes that this chlorophyll is a synthetic production, and 

 suggests that it may be used for protective purposes, but that pro- 

 bably a pigment of less complicated chemical constitution might 

 answer as well. Of course this would not apply to the derived 

 (and modified) chlorophyll of Phytophagous larvae. 



Dr. MacMunn's interesting discovery of entero- chlorophyll (which 

 he believes to be synthetically formed) in the liver of many inverte- 

 brates, does not apply to the present question. (See " Proc. Roy. Soc," 

 vol. 35, No. 226, p. 370.) 



2. Methods by which the two Factors of Larval Colouration may he 

 Recognised : Instances of their Occurrence. 



If the body of a small individual of the green form of a dimorphic 

 (green and brown) Noctua larva be gently compressed, the green tint 

 disappears from this part, and is replaced by faint yellow. The 

 markings of the larva (apart from the ground colour) are unchanged. 

 At the same time the tracheal system and other internal structures 

 become easily visible. Conversely, the swollen uncompressed part of 

 the body becomes of a far deeper green than it was before. This is 

 especially well seen in the true legs, of which the colour is normally 

 pale. Such effects are due to the fact that the green colour depends 

 upon the green blood. (I use this word for the more correct term, 

 haemolymph.) This conclusion is confirmed by examining the blood 

 itself, and by observing that the green ground colour of the larva dis- 



