2l6 



HAROLD HEATH. 



verse blood sinus (sinus transversus) with a dorsal disk-like cav- 

 ity in contact with the ventral pericardial wall (Fig. 2). From 

 the antero-lateral border of each of these last-named spaces a 

 slender tube arises and passing outward plunges beneath the 

 afferent branchial sinus and then curving backward gradually 

 approaches the surface of the body and opens through the renal 

 papilla. The position of the external excretory opening is, 

 unlike that of the genital papilla, remarkably constant in position. 

 In one hundred specimens examined on this point the excretory 



Fig. 2. Posterior part of kidney of C. stellcri. The ventral wall has been removed 

 and a portion of the dorsal in order to show the transverse sinus (s) and the exit of 

 the ureter; ba, branchial artery ; e, outer kidney opening ; g, gill ; r, renal pericar- 

 dial opening; genital opening opposite eighth gill. 



pores were, with a very few slight exceptions, situated opposite 

 the last gill. 



Connective tissue cells laden with concrements, such as were 

 described by Brock ('83) for several molluscs, are present in 

 Cryptochiton in great abundance. In all specimens, but notably 

 those above 10 cm. in length they form great accumulations in 

 the foot and mantle in the vicinity of the mantle furrow and give 

 the tissue the appearance of having been charged with light yel- 

 low sand which cuts with a distinctly gritty sound. Cells of this 



