A MANUAL OF ZOOLOGY 31. 



the margin of the mantle ventrally? Are there any indi- 

 cations of cartilage on the siphon? If so what is its use? 

 Open the animal along the mid-ventral line. The two 

 sexes differ in that the nidamental glands of the female, 

 cover the other organs and give, the appearance of a 

 thick, granular substance. Notice four large muscles that ■ 

 attach the head to the mantle; two dorsal retractors of 

 the head and two ventral retractors of the siphon. A 

 pair of silvery cords will be seen extending from the neck, 

 just posterior to the dorsal mantle cartilage, to the mantle. 

 These are nerves which terminate in large ganglia on the 

 inner surface of the mantle. 



Are there any cartilage formations on the siphon? Jf 

 so is there anything on the mantle corresponding to the 

 same? 



Note the two valve-like sacs lateral to the siphon 

 sac which is on the mid-ventral line. Does their shape 

 and position suggest their use? 



Find the rectum and the anal opening directly posterior' 

 to the siphon. Is J;here a mesenteric fold to keep the 

 viscera in placB? JLiook for the ink sac immediately dorsal 

 to the intestine. Find the duct and opening from this. sac. 



At the' end of an elongated papilla which lies parallel 

 to the intestine, and on the right side will be found , the 

 opening of the male reproductive system. Find a pair of 

 papillae, about an inch from the anal opening, which are 

 openings for the renal organs. Trace the ducts, if possible, 

 posteriorly to the renal organs. 



Look for the gills 'on either side of the mantle cavity. 

 How many are, there? How are they located as to the 

 retractors of the . siphon? Notice a vein running from 

 the renal organ to the gill, (branchial vein). Find the 

 branchial heart, a small, oval, white body at the base of 

 each gill. 



From a point midway between the branchial hearts 

 notice a narrow menxbrane-like cord coming off and pass- 

 ing across the mantle cavity to the mantle. ■ Does it have 

 any branches after it reaches the mantle? This supplies 

 the mantle with blood and is called the median mantle 

 artery. Find the lateral niantle ■ arteries. Posterior to 

 theac arteries find a laree sac reaching to the nosterior 



