72 GRIFFIN. 



will issue from the skin; at the same time the pigmentation 

 disappears. The black pigment of these spots can all be pressed 

 out, coloring the water purple as it appears, until the skin is 

 white. 



The renal pore is located in the pigmented area at the posterior 

 extremity of the mantle ridge. 



The true mantle cavity extends farther beneath the base of 

 the gill than is at first apparent. The dotted line in text figure 

 1 indicates the limit of the mantle cavity. From this it will be 

 seen that a considerable part of the pericardium and of the 

 nephridium is included in the base of the mantle. 



The branchia is large (65 millimeters long, 25 millimeters 

 wide, and 15 millimeters thick). It is attached to the mantle 

 and body wall by a broad base which follows approximately the 

 curve of the mantle ridge. The free extremity of the branchia 

 curves to the right and backward, ending well back of the anal 

 papilla. Both dorsal and ventral sides of the branchia are sub- 

 divided into leaflets, upon the outer edges of which the afferent 

 branchial veins are prominent. The dorsal and ventral series of 

 leaflets are widely separated by a deep groove on the anterior 

 face of the branchia. The color of the branchia is gray or 

 greenish, punctate with numerous black dots. 



The anal papilla stands just below the exhalent siphon and 

 within the arc of the posterior side of the gill. Within the in- 

 spiratory aperture and a little to the right is the opening of 

 the vulva. The thin-walled pericardium occupies the area on the 

 left side of the body between the mantle ridge and the anterior 

 margin of the branchial chamber. The triangular nephridium 

 forms the posterior border of the pericardium, and extends back- 

 ward as far as the posterior extremity of the mantle (fig. 8, 

 Plate II) . The visceral mass back of and below the kidney is 

 covered by a thin, semitransparent body wall, which is pigmented 

 in extremely fine black dots. The outlines of the liver and her- 

 maphrodite gland, and portions of two coils of the intestine can 

 be seen through the kidney and pericardium. 



On the right side of the branchial chamber, we find beneath 

 the branchia and in front of the anus, an elevation caused by a 

 portion of the reproductive system (the "anterior genital mass") . 



The hypobranchial gland consists of an area of dermal glands 

 which lie in the floor of the branchial cavity, commencing at 

 the right side of the genital orifice, and extending backward 

 along the right side at least as far as the level of the anal papilla. 

 The thickening of the dermis in the glandular area is noticeable ; 



