PNEUMONECES 71 



organs that characterize free-living animals. Some Trem- 

 atodes are parasitic upon the outside (or ectoderm) of other 

 animals, and are hence called ectoparasites. 



PNEUMONECES 



This form is found as a parasite in the lungs of frogs. 

 In some localities a large proportion of the frogs are infested 

 and several specimens are frequently found in one frog. The 

 host of the asexual generation of this species is not known, 

 but in a closely allied species the asexual generation lives in 

 the pond snail. The living worm is cylindrical and pointed 

 at both anterior and posterior ends. With a low-power ob- 

 jective note: 



1. The anterior sucker, surrounding the mouth. 



2. The ventral sucker, near the middle. 



3. Whether eyes are present or not. 



4. The alimentary canal, 

 (a) The mouth. 



{b) The muscular pharynx. 



(c) The intestine which, soon after leaving the pharynx, 

 divides into two equal branches, passing 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 Bdelloura. 



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 pos- 

 terior to the median sucker. Here it divides and sends a 

 branch on either side of the worm to near the anterior end. 



The Nervous System. — This is difficult to see, but in a 

 mounted specimen a small, deeply stained mass, the cerebral 

 ganglia, may be visible on either side of the pharynx. Three 

 pairs of longitudinal nerves pass back to near the posterior 

 end of the body. 



Make a drawing showing the above structures indicating 

 all you have been able to observe. 



