PHYSIOLOGY OF THE INVERTEBRATA. 165 



before the second (Fig. 31, sp. i). Considering the chemical 

 change which must have taken place in the chlorophyll 

 during digestion, rendering possible the passage of the walls 

 of the digestive tract, and considering its chemical union with 

 a proteid constituent of the blood, the resemblances of the 

 spectra are very striking ; in fact, the two spectra are far 

 nearer to each other than the ordinary spectrum of chloro- 

 phyll in alcoholic solution is to the unaltered chlorophyll of 

 leaves." 



Alcoholic solutions of chlorophyll are very unstable, the 

 reason being that the alcohol precipitates the proteid which 

 was orginally united to the colouring matter in the living 

 plant or animal. Consequently, in the alcoholic solution the 

 combination is no longer the same. 



Both the chlorophyll and xanthophyll in caterpillars' blood 

 are united chemically with a proteid ; hence their great 

 stability. The separation of these pigments from the proteid 

 is at once efEected by the addition of alcohol. The former 

 pass into solution, while the latter is precipitated. The 

 solution of the pigments is very fugitive ; an alcoholic 

 solution of chlorophyll changing in a few seconds, so rapidly 

 is it acted on by light. 



" But while the pigments exist unchanged in the blood of 

 many larvte for a long time, in other species they are entirely 

 destroyed during the comparatively short period preceding 

 ecdysis, when some green larvae become brown ; and con- 

 versely the pigments may appear in the blood equally suddenly. 

 The former change must be due to an active destruction or 

 excretion of the pigments, and is probably also accompanied 

 by changes in the digestive tract, whereby no more pigment 

 is passed through its walls. And so also the proportions of 

 xanthophyll and chlorophyll may be changed during the life 

 of a caterpillar." 



From Poulton's interesting investigations it will be observed 

 that Lepidopterous larvas and pupae make use of a modified 

 chlorophyll, as well as other plant pigments^ derived from 



