538 



ZOOLOGY 



methods, the total number of gills, viz., eighteen complete gills 

 with two vestiges and seven epipodites. 



\ 



d 



The excretory organs differ both in position and in form 



from those of 

 Apus. There are 

 no shell-g lands, 

 but at the base 

 of each antenna is 

 an organ of a 

 greenish colour, 

 the antennary or 

 green gland, by 

 which the function 

 of renal excretion 

 is performed. The 

 gland (Fig. 445) is 

 cushion - shaped, 

 -/> and consists o f 

 three parts (1) a 

 central saccule (s.) 

 of a yellowish 

 colour, occupying 

 the mid - dorsal 

 region, and con- 

 sisting of a sac 

 divided into 

 numerous c o m - 

 partments by par- 

 titions, and com- 

 municating with 

 (2) the outer or 

 cortical portion 



I '!(-. -i }.>. Diagram of kidney of Astacus fluviatilis. I, un- / ^ \ of a arppn 



ravelled ; II, the parts in their natural relations, bl. bladder ; V"P')} l l P. 



. j>. cortical portion.; d. duct; s. saccule; c. p. white por- colour, Consisting 

 tion. (After Marchal.) 



