608 F. W. GAMBLE AND ¥. W. KEEBLE. 



a store of (chiefly) blue pigment^ which takes no part in the 

 superficial coloration of the animal. 



We turn now to the detailed examination of the " chroma- 

 tophores " themselves, and for the purpose we select a pig- 

 ment spot from one of the transverse bars on the abdomen. 

 Occasionally such a spot or '^ chromatophore " has a distinct 

 central " body " from which run branching and anastomos- 

 ing processes; more usually (PI. 34, fig. 19) there are two 

 densely coloured and ill-defined central portions of a red 

 colour by transmitted light. The processes are either red or 

 yellow, finely branched, and, in places, continuous with those 

 of adjacent '' chromatophores." By means of a high power 

 the processes are seen to be tubes with a distinct wall, a 

 feature most readily ascertained when the pigment has 

 broken down into small globules separated by clear spaces. 

 We have repeated this observation on a great number of 

 "chromatophores" from different colour varieties, and 

 though the finer arterial branches resemble chromatophoric 

 processes free from pigment, the large blood-corpuscles in 

 the arteries and the indubitable presence of pigment granules 

 in the intact processes readily serve to distinguish these 

 structures. In fact, with practice, the translucent, branched 

 tubes can be seen radiating from a " chromatophore " whose 

 pigment is retracted into the central " body." The " chro- 

 matophore " is a structure whose outline is fixed, — that is to 

 say, the processes are limited by a definite membrane. 

 Colour-changes in the animal are caused by movements of 

 the pigment within the chromatophores, movements which 

 may be modified by nervous impulses, but of the nature and 

 origin of which we know nothing. 



Summarising the more striking features of these colour 

 elements in a red-lined Hip poly te varians, we may point to 

 the presence of red and yellow pigment (and to anticipate, 

 we may add blue) in the same " chromatophore ; " the close 

 relation of these colour elements to certain organs, and par- 

 ticularly to the vascular system ; the tubular nature of the 

 processes and flowing movement of the pigments ; and the 



