BTJSYCON. 131 



15. The gonad, which is borne on the dorsal surface of the 

 liver, and differs in individuals from red and brown to yellow. 



16. The stomach, which lies on the left (external) surface of 

 the liver. It is curved and light colored and is frequently rather 

 indistinct. 



17. The kidney, which lies on the dorsal surface, and a little 

 to the left side, on the anterior end of the liver. It is somewhat 

 rectangular in shape and differs in color from a yellowish-brown 

 to a chocolate color. The kidney is composed of two parts, 

 the large acinous portion, and the smaller tubuliferous portion. 

 The latter lies along the left side of the former, by the side of 

 the pericardium. 



18. The pericardium lies to the left of the anterior end of 

 the kidney. Through its dorsal wall the yellowish heart can 

 generally be seen. 



19. The columellar muscle, which attached the animal to its 

 shell and enabled it to withdraw, can be traced to the foot. 



20. If the specimen being examined is a female, the large 

 yellowish nidamental gland will be seen near the right side. 



21. The large, brownish gill lies to the left of the nidamental 

 gland in the female and anterior to the heart. 



22. The osphradium is a small, brownish organ to the left 

 of the anterior end of the gill and at the base of the siphon. 



23. The hypobranchial gland is a glandular portion of the 

 mantle, to the right of the gill (between the gill and the nida- 

 mental gland, in the female). 



Make a drawing of the animal as a whole, showing as many 

 of the observed points as possible. 



Open the mantle chamber by cutting the mantle along the 

 right side of the gill to the limit of the cavity, reflect the flaps, 

 and notice the position and structure of the gill, osphradium, 

 hypobranchial gland (cut in opening the mantle cavity), and, if 

 the specimen is a female, the nidamental gland. The open- 

 ing of the rectum will be seen at the end of a short papilla 

 in the right side of the mantle cavity. The opening of the 

 nidamental gland will be seen on an elevation a little to the right 



