132 INVERTEBRATE ZOOLOGY 



pancreas ; the intestine, which leaves the stomach near the point 

 where the oesophagus enters it ; the rectum, which is joined by 

 the ink-bag and passes to the anus. 



Exercise 4. Take the alimentary tract out of the body, pin it 

 down, and make a drawing of it ; label all its divisions. 



Slit open the stomach and examine its ridges. Slit open the 

 pharynx on the upper side ; note the large chitinous jaws and 

 the radula. The latter organ, like the radula of snails, is used 

 in chewing the food ; examine its surface under a microscope 

 and note the calcareous teeth. 



Exercise 5. Make a drawing of the jaws. 



Exercise 6. Draw several of the teeth of the radula. 



The reproductive system ; the male. The principal genital organs 

 have already been observed. The single median testis is a large, 

 flat organ, dorsal to the stomach pouch, in the hinder portion of 

 the visceral mass ; the genital artery joins it with the surface 

 of the stomach. The testis has no direct connection with 

 the vas deferens, but is surrounded by a thin transparent mem- 

 brane within which it lies as in a capsule, and into which the 

 spermatozoa escape. The vas deferens, which is also unpaired, 

 communicates with this capsule. It is a long and much-twisted 

 tube with several wide glandular regions, and lies, bound by 

 connective tissue into a compact mass, on the left side of the 

 viscera. Take the entire system out of the body, put it in 

 water, loosen and straighten out, so far as possible, the con- 

 volutions of the vas deferens. Beginning with its hinder end 

 we find first a narrow, convoluted tube, then follows a thicker 

 tubular portion, the vesicula seminalis ; near the forward end 

 of this portion is a glandular body, the prostate gland, and a 

 membranous sac; a long, straight, narrow portion comes next, 

 which widens to form the spermatophoric sac, within which 



