CRUSTACEA 



343 



phores), but some of the blue, and perhaps of certain others, is 

 diffused in the tissues. The chromatophores may He in the epidermal 

 layer, in the dermis, or in the connective tissue of deeper organs. Their 



aes 



op.- 



Fig. 227. The antennule of Astaais. A, The right antennule, seen from the 

 median side with the basal joint opened and the flagella cut short. B, Two 

 joints of the distal part of the outer flagellum, enlarged, after Huxley. C, The 

 basal joint of the left antennule, from above. D, Two hairs from the stato- 

 cyst. E, An aesthetasc. aes. aesthetasc ; en. inner flagellum ; ex. outer flagellum ; 

 grn. sand grains; w. nerve; n.f. nerve fibre; op. opening of statocyst, overhung 

 by a fringe of hairs ; stc. statocyst. 



behaviour has been studied in various malacostracans. The pigment 

 is often caused to expand or contract, which it does by flowing into 

 and out of their processes. In this it is affected by light, responding 

 both to intensity of illumination and to the nature of the background, 



