48 PLATYHELMINTHES. 



the nervous system and pharynx. What relation have the nerve 

 cords behind? 



5. With the high power and good light, look for the water- 

 vascular tubules. These tubules are more easily seen in speci- 

 mens that have been under the cover-slip some time. The 

 region anterior to the cerebral ganglia is a favorable place. 

 They form a clear, branching tracery, a little lighter than 

 the surrounding tissue. The flicker of the flame cells can 

 usually be seen, but they may be more easily seen in Crosso- 

 bothrium. Examine chart and test-book figures of the water- 

 vascular system. 



Make a good-sized drawing of a worm, showing the above 

 points. 



Reproductive Organs. Turbellarian worms are hermaphro- 

 ditic. In this form the various organs are so crowded together 

 that it will be best to follow each system separately. Com- 

 press a specimen under the slip and find the male organs as fol- 

 lows: 



(a) The testes are the numerous rounded masses between 

 the lateral branches of the gut. They are connected by means 

 of fine tubes which cannot be seen in fresh specimens. 



(b) The vasa deferentia, two large tubes, one on either side 

 of the pharynx, that unite posteriorly near the base of the penis. 



(c) The genital atrium, within which the penis lies with- 

 drawn, is situated behind the pharynx. The penis and atrium 

 may be considered as a replica, in miniature, of the pharynx 

 and its sheath. 



If the above structures cannot be satisfactorily seen, try 

 preserved, stained, and mounted^ specimens. 1 



1 Specimens may be readily killed by compressing under a slip, being 

 careful to draw the excess of fluid out on one side so that the animal 

 cannot contract, and running in killing fluid. (Sublimate acetic is good.) 

 As soon as they become opaque white, put on enough killing fluid to float 

 the slip off and transfer the specimens to a dish of the fixative for five 

 minutes, then 50 percent alcohol a few minutes, 70 percent several hours, 

 stain with borax carmine or Delafield's hematoxylin; dehydrate, clear and 

 mount in balsam. (See directions in the appendix for making permanent 

 preparations.) 



