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



1. The Essential Nature of the Colouring of Phytophagous Larvce. 



Phytophagous larva? owe their colour and markings to two causes : 

 (1) Pigments derived from their food-plants,* chlorophyll and xantho- 

 phyll, and probably others; (2) pigments proper to the larva?, or 

 larval tissues made use of because of some (merely incidental) aid 

 which they lend to the colouring, e.g., fat. A larva may be coloured 

 by either or both of these groups of factors. It may be generally 

 stated that all green colouration without exception, as far as I have 

 investigated the subject, is due to chlorophyll ; while nearly all 

 yellows are due to xanthophyll. All other colours (including black 

 paid white) and some yellows, especially those with an orange tinge, 

 are due to the second class of causes (as far as I am aware : it is, 

 however, extremely probable that certain colours will be proved to 

 arise from the modification of the derived pigments ; and many obser- 

 vations make it probable that other colours may be derived from 

 plants in the case of larva? feeding upon the petals, &c). The 

 derived pigments often occur dissolved in the blood, or segregated in 

 the subcuticular tissues (probably the hypodermis cells), or even in a 

 chitinous layer, closely associated with the cuticle itself. This last 

 situation has only as yet been proved in the case of the pupa of 

 Papilio Machaon, but it is almost certainly true of many other pupa?. 

 The colours proper to the larva? occur in the hypodermis cells and in 

 the cuticle. The commonest structural basis of variability or poly- 

 morphism in larva? is afforded by the varying extent to which either 

 of these factors takes part in producing colouration. Thus brown 

 and green are by far the commonest instances of dimorphism, and 

 when this is the case the former is due to larval pigment, the latter to 

 derived plant pigments. It is very remarkable that there should be 

 such an essential difference between the larva? from the same batch of 

 esrgs, as far as the causes of colour are concerned. Mr. Raphael 

 Aleldola has very conclusively argued for chlorophyll as the cause of 

 the colour in green larva? in a paper in the " Proc. Zool. Soc." for 



* It will be shown that the derived chlorophyll of larvae has undergone chemical 

 changes of which the effects appear in the altered spectrum, and in the great 

 stability of the pigment when present in the animal blood or tissues. If, on the 

 other hand, the chlorophyll be separated from the proteid with which it is united in 

 t he animal, it is so unstable that the colour disappears at once, and it is impossible 

 1 o obtain it in solution by the xise of the ordinary solvents of vegetal chlorophyll (or 

 by any reagents of which I have made use). The spectrum and chemical characters 

 are very constant, seeming to prove that the same definite changes are wrought by 

 many species of insect. At the suggestion of Professor E. Ray Lankester, I 

 propose to call this derived pigment metachlorophi/ll. The spectrum of the green 

 blood of the pupa of JEphyra JPanctaria differs from that of other larvae and pupa? 

 hiiherto examined, and I propose for this form of derived pigment the term JEphyra- 

 chlorophyll. There is not at present sufficient ground for giving a distinctive name 

 to the derived xanthophyll. — May 4th, 1885. 



