606 F. W. GAMBLE AND F. W. KEEBLE. 



repositories of these pigments, which matters appear to have 

 received hitherto curiously little attention. For the present 

 we shall regard the condition of a colour form as fixed, re- 

 serving the account of the chromatophoric changes effected 

 by light and other stimuli for Section IV. 



If a red-lined variety is examined under a low-power 

 objective by light transmitted through an Abbe condenser, 

 the colours — except for the green or yellow patches formed 

 by the stomach and liver and for any food substances in the 

 intestine — are seen clearly to be due to masses of " chro- 

 matophores." The chitinous investment and the epidermis 

 being transparent and colourless allow the muscles, 

 alimentary tract, the gills, heart, and blood-vessels, to be 

 plainly perceived (PI. 34, fig. 14). The median dorsal and 

 ventral stripes of red colour are due to masses of pigment 

 closely associated with the alimentary canal and nerve-cord 

 respectively, and require deep focussing for their satisfactory 

 definition ; while the transverse bars which run across the 

 body near the hinder edge of each segment are composed of 

 red and yellow pigment spots placed nearer the surface of 

 the body, though it is easy to determine that they are not in_, 

 but below the epidermis. Closer examination shows, in fact, 

 that the bodies of all the " chromatophores " lie in the 

 connective tissue, and are definitely related to the digestive 

 system, and especially the " liver," the vascular and muscular 

 systems (PL 34, figs. 14, 15, 19, and PI. 35, fig. 23). 



Thus, as the peristaltic waves of contraction pass along the 

 alimentary canal, scattered chromatophores move with the 

 walls of the gut, though for the most part the pigmented 

 sheath attached to the wall of the great intestinal venous 

 sinus (in which the blood is slowly travelling forwards to- 

 wards the heart) remains stationaiy. In a similar manner, 

 the ventral layer of "chromatophores'^ surrounding the 

 nerve-cord is connected with the walls of the ventral blood- 

 sinus. The pigment spots forming the transverse bars lie 

 between the intermuscular arteries and venous spaces, and 

 are frequently closely attached to the walls of the arteries, 



