On the Colours of certain Lepidopterous Larvce. 417 



cules of hydrogen when this body is compressed to a density com- 

 parable with the density of liquids.* 



" The Experimental Proof that the Colours of certain Lepido- 

 pterous Larvae are largely due to modified Plant Pigments 

 derived from Food." By EDWARD B. PouLTON, M.A., F.R.S. 

 Received May 12, Read June 8, 1893. 



[PLATES 3 AND 4.] 



In a paper printed in the * Proceedings of the Royal Society ' for 

 1885 (pp. 269 315), I brought forward many reasons for regarding 

 certain elements of the colouring of Lepidopterous larvae as modified 

 chlorophyll derived from the food plant. For this altered pigment 

 the name metachlorophyll was suggested (Zoc. cit., p. 270). Many 

 other observations, subsequently made, supported the same conclu- 

 sion; but it was not until the summer of last year (1892) that I was 

 able successfully to carry out the critical experiment, viz., selecting a 

 species of larva which normally eats green leaves, to feed it from the 

 egg upon parts of the plant from which all colouring matter is 

 absent. 



This experiment was carried out in the following manner : 



A captured female of Tryphcena pronuba laid many hundreds of 

 eggs in a chip box. The first larvae began to appear September 7, 

 1893. On this and the subsequent dates, the larvae intended for the 

 purposes of these experiments were arranged in three sets, fed re- 

 spectively upon (1) the yellow etiolated leaves from the central part 

 of the heart of the cabbage, (2) the white mid-ribs of such leaves 

 from which the yellow blade was carefully removed with scissors, 

 (3) the deep green external leaves of the same plant. 



In all other essential respects the conditions of the three sets were 

 the same. All were kept in the dark to prevent the change of the 

 etiolin into chlorophyll. They were only exposed to light during the 

 times necessary for comparison and feeding, and these are indicated 

 below. A few were kept in glass cylinders standing on plates, the 

 majority being confined in white earthenware pots covered at first 

 with white muslin, but subsequently with glass sheets. Eventually 

 all were kept in pots. 



It is clear that the only essential difference between the conditions 

 of the sets was the fact that the food of the first contained etiolin but 



* Lord Kelvin states that in " any ordinary liquid " the mean distance between 

 the centres of contiguous molecules is, with a " very high degree of probability," 

 less than 0*000.0002 and greater than O'OOOOOOOOl of a centimetre. See ' Eoy. 

 Institution Proc.,' vol. 10, p. 185. 



