APPENDIX IV 



EXCRETION 



The Shell Gland. The shell gland falls easily into 

 three typical sections (Fig. 30, p. 125); the terminal 

 saccule, the urinary canal, and the urinary duct with 

 the bladder. The terminal saccule is branched and 

 irregular, and lies in the blood stream between the 

 central coils of the urinary canal. As far as we could 

 judge from our material it seemed to be lined by large 

 flat granulated cells, resting upon a fine basal membrane. 

 It is difficult to say if the large vacuoles to be seen in many 

 of them are natural. 



The urinary canal shows the structure depicted in Fig. 68, 

 which is characteristic of the antennal gland of the other 

 Crustacea. Grobben described the striped appearance as 

 being due to protoplasmic strands arranged vertically on the 

 basal membrane owing to the active streaming from without 

 into the lumen of the tube. Tangential sections of the mem- 

 brane, however, show it to be an independent spongy struc- 

 ture, like hardened foam (see Fig. 68, to the right), forming 

 a strong but very porous support to the large flat epithelial 

 cells. Grobben figures the nuclei as imbedded in this 

 striped membrane. In Apus, however, they lie with their 

 surrounding protoplasm on the membrane, here and there 

 heaped up, or even artificially torn away, in both cases 

 leaving the membrane intact, which would hardly have 



