132 INVERTEBRATE ZOOLOGY 
pancreas; the intestine, which leaves the stomach near the point 
where the cesophagus 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 
