1885.] Colouring of Phytophagous Larvce. 273 



appears on removing the bright green blood. If, on the other hand, 

 a brown variety of the same larva be compressed, the results are 

 much less marked, and chiefly dependent upon the difference in 

 transparency of the compressed and swollen parts of the larva. The 

 blood is generally found to be colourless or very faintly yellowish : 

 hence the ground colour of the green form depends upon its blood, 

 while that of the brown form depends upon its proper pigment. 

 Intermediate colours are produced by intermediate conditions, and it 

 is quite common to find a series connecting the green and brown 

 larvae. On compressing a greenish-brown larva, the green at once 

 becomes apparent in those parts of the organism which are deficient in 

 pigment, i.e., the under surface and claspers ; and indeed it may bo 

 generally stated that the colour due to the blood generally pre- 

 dominates in the lower part of the body, while that due to larval 

 pigment usually predominates on the back. The most extreme brown 

 varieties have often lost all colour in their blood (except when it is seen 

 in a very thick layer). Phlogophora Meticulosa is a common species 

 upon which these observations can be made. Not only are these two 

 factors so variably developed in dimorphic or polymorphic larvae, but the 

 same variability is very commonly seen in a single life-history. Thus 

 many green larvae become brown after one of the ecdyses, or brown 

 ones become green. Hence in the period preceding ecdysis the blood 

 must have lost its colour (P. Meticulosa and many Noctuae), or the 

 larval pigment must have become so opaque as to obscure any more 

 deeply placed colour (common among Geometers). There are often 

 great advantages to be gained by a brown larva retaining the green 

 colour in its blood. This is well seen in the case of Bnnomos Angularia, 

 of which the larva is an opaque Geometer, resembling the dark twigs of 

 the elm. The pupal period is very short (in the middle of the summer), 

 and the cocoon is consequently very slight. It is formed of a few 

 leaves loosely bound together, between which the larva and afterwards 

 the pupa, are easily seen. Here therefore the brown colour is inappro- 

 priate, and the whole of the larval pigment is discharged, allowing the 

 green blood to give its colour to the larva during the quiescent period 

 before pupation. The pupa is similarly coloured and is also green. 

 (It is dimorphic, with two shades of green. These facts about E. 

 Angularia have been communicated to the Entomological Society in a 

 hitherto unpublished paper, but the explanation has not appeared 

 before.) Furthermore, these larvae, when very young, live upon the 

 surface of the leaf they are eating, and at this time they are coloured 

 green by their blood, the pigment having not yet been deposited in a 

 sufficient amount to render the surface opaque. Hence the alterna- 

 tion of colours, which follows the corresponding succession of objects 

 imitated, depends upon the shifting scenes resulting from the presence 

 of green blood behind a superficial covering, which can be rendered 



