132 PHYSIOLOGY OF THE INVERTEBRATA. 



is not due to the flat, oat-shaped, granular corpuscles with 

 their well-defined walls and nuclei, but is due to the liquid in 

 which they float. 



In the case of Phytophagous larvae, Mr. E. B. Poulton, 

 r.R.S.,* has shown that they owe their colour and markings 

 to two causes: — (l). "Pigments derived from their food- 

 plants, chlorophyll and xanthophyll, and probably others ; 

 (2) pigments proper to the larvfB or larval tissues made use 

 of because of some (merely incidental) aid by either or both 

 of these groups of factors. It may be generally stated that 

 all green colouration without exception, is due to xantho- 

 phyll. All other colours (including black and white) and 

 some yellows, especially those with an orange tinge, are due 



to the second class of causes Derived pigments often 



occur dissolved in the Mood, or segregated in the subcuticular 

 tissues (probably the hypodermic cells), or even in a chitinous 

 layer, closely assocrated with the cuticle itself." 



In some cases, the colour of the blood changes before the 

 pupal stage is reached, while in others it remains the same 

 as in the larval condition. On this point Mr. Poulton {Joe. 

 cit., p. 277) says : — " the superficial derived pigments of 

 Sphinx Lifjustri become brown in the dorsal region, before 

 pupation, while the colour of the blood is unchanged. In 

 Dicranvra Vimda the whole larva becomes reddish-brown, 

 and in this case the green blood changes to brownish-yellow. 

 The true larval pigment also changes before pupation, except 

 when it is cuticular. Thus the larva of E. Anr/ularia 

 becomes transparent by the disappearance of dark pigment, 

 and the green blood gives its colour to the larv^a. The green 

 colour of the blood is generally retained in the pupal state, 

 and it is often of great importance." 



According to Mr. Poulton, the blood of Phytophagous larvae 

 and pupa3 is acid to litmus-paper, with the exception of 

 that of Ejthyra 2'>unctaria, which seemed to be neutral. This 

 acid, which is volatile, is readily extracted with ether ; but its 



* Proc. Itoy. /Sue, 1S85, p. 270. 



