302 APPENDIX IV 



been the case if the striation were really due to strands of 

 protoplasm free in the cells. There is no trace in Apus of 

 a chitinous cuticle lining the canal. 



The nuclei of the epithelium are very large and oval, the 

 longest diameter being 40-45^ (in a specimen of A. cancri- 

 formis), i.e. slightly larger than the nuclei of the nutritive 

 cells of the eggs, a sign of their great physiological activity 

 in the economy of the animal. 



The urinary canal shows a slight widening as it bends 



n 



FIG. 68. Part of a section of the urinary canal (shell gland of Apus). bin, basal 

 membrane on which rests the harder supporting framework, seen in tangential 

 section (at is) to have a spongy structure;^, inner layer of protoplasm; n, 

 nuclei with numerous clear round nucleoli. 



down towards the ventral side. We at first thought that 

 this might be the bladder, but there is no change in the 

 character of the epithelium. At the base of the second 

 maxilla, this wider portion leads through a very narrow 

 chitinous canal into the true bladder, which is a chitin-lined 

 sac in the shaft of the limb. The chitinous lining of the 

 bladder, which distinguishes it from the urinary canal, makes 

 it a suitable reservoir for excretory fluids. 



The opening of the duct at the tip of the second maxilla 

 is shown in Zaddach's drawing as a point which he, however, 



