40 PLATYHELMINTHES. 



snail. The living worm is cylindrical and pointed at both an- 

 terior and posterior ends. With a low-power objective note: 



1. The anterior sucker, surrounding the mouth. 



2. The ventral sucker, near the middle. 



3. Do you find eyes ? 



4. The alimentary canal. 



(a) Mouth. 



(b) The muscular pharynx. 



(c) Soon after leaving the pharynx the intestine divides 

 into two equal branches, which pass, one on the left and one on 

 the right side, to near the end of the body. These intestinal 

 branches do not send out lateral branches as they do in Bdel- 

 loura. 



The Water-vascular System. — A small opening will be found 

 at the posterior end of the body from which a duct passes forward 

 in a median position to a point a little posterior to the median 

 sucker. Here it divides and sends a branch on either side of 

 the w^orm to near the anterior end. 



The Nervous System. — This is difficult to see, but on either 

 side of the pharynx a small, deeply stained mass, the cerebral 

 ganglia, may be visible. Three pairs of longitudinal nerves pass 

 back to near the posterior end of the body. 



Make a drawing showing the above structures as far as you 

 have seen them. 



The Reproductive Organs. — Male: Two large bodies, the 

 testes, very definite in outline, occupy the posterior end of the 

 worm. A duct from each, the vas deferens, passes forward, 

 and the two unite just posterior to the point where the intestine 

 branches. By means of a median, common duct, they open 

 to the exterior through the inale genital opening. This is situ- 

 ated on the ventral surface, just below the point where the 

 intestine branches. 



Female: Some of the ducts are difficult to see, and in many 

 cases they cannot be followed, but some of the organs can be 

 found in most of the specimens. 



The ovary is a lobed organ lying a little to one side of the 



