56 THE CRAYFISH [CH. II 



utilised in giving colour to the outer shell. Cue'not 1 has 

 shown, by employing meat stained with various dyes, that 

 the ' liver ' tubules are concerned in the absorption of 

 food, much of the coloured meat passing into them. This 

 observation is confirmed by McMurrich's 2 work on ter- 

 restrial Isopod Crustaceans. Saint Hilaire 3 has proved 

 that peptone is not absorbed by the intestine, and that if 

 injected in small quantity into the body spaces it is taken 

 up by the ' liver ' : in large quantity it causes death. Fats 

 on the other hand are absorbed by the epithelium of the 

 mid-gut and its dorsal diverticulum. The ' liver ' is further 

 of service in regulating the percentage of water in the 

 blood, and in addition lays up stores of fat and glycogen. 

 A structure known as the dorsal pyloric valve carries 

 undigested and indigestible solids across the cavity of the 

 mid-gut, whose epithelium is very delicate, direct into the 

 intestine. 



Respiration is carried on by means of the branchial 

 plumes which project outward from the legs or sides of the 

 thorax into the water, and are covered by a protecting fold 

 of the shell (branchiostegite) so as to be practically 

 enclosed in a chamber through which the water is wafted 

 from behind forward in a steady flow by the sculling 

 movements of the ' scaphognathite ' (the united exopodite 

 and epipodite of the second maxilla), at the anterior end of 

 the branchial chamber. The apex of the endopodite of 



1 C. R. Acad. Sci. Paris, torn. 116. 



2 Journ. Morph. xiv. p. 102. 



3 Bull. Acad. R. Belg. (3) xxiv. p. 506; cf. also Stamati, Bull. Soc. 

 Zool. Fr. xm. p. 146. 



