spots, while the other two extend laterally and posteriorly. There 

 is no anus. 



III. THE REPRODUCTIVE SYSTEM. 



The two sexes are united in the same individual, the common 

 sexual opening being seen in the mid-ventral line a little posterior 

 to the proboscis. The ovaries lie in the anterior portion of the body, 

 one on either side. The ducts may be seen leading from them toward 

 the external opening. Yolk glands appear as tabulated structures 

 lying between the ramifications of the intestine. The testes are 

 rounded glands scattered along the sides of the body from the 

 anterior to the posterior ends. Do you find ducts leading from them? 

 Along each side of the proboscis sheath is a tubule, the ras dcfercns 

 which runs into the common sexual opening. 



IV. NERVOUS SYSTEM. 



In favorable specimens the nervous system can be easily followed 

 as a series of whitish lines and areas. The two eye spots mark 

 the situation of the cerebral ganglia, each ganglion appearing as an 

 irregular mass which sends a nerve posteriorly, and several smaller 

 ones anteriorly, and laterally. The right ganglion is connected with 

 the left by a commissure. Follow the lateral nerves posteriorly ; 

 they will be found to unite at the hinder end of the body. Are the 

 lateral nerves above or below the branches of the alimentary canal? 

 Study sections through the eye spots. 



V. THE MUSCULAR SYSTEM. 



The muscular system is especially developed in the region of the 

 pharynx. Muscle fibres also occur under the integument, the outer- 

 most layer consisting of circular fibres while there are two inner 

 layers of longitudinal fibres separated by a layer of parenchyma. 

 Many diagonal fibres are also found running from the dorsal to the 

 ventral side. 



VI. EXCRETORY SYSTEM. 



Along the sides of the body parallel to the longitudinal nerves is 

 a branched system of very small and clear tubules, the water vascu- 

 lar or excretory system. These tubules open to the exterior at many 

 points along the dorsal surface and are difficult to trace. 



Study prepared sections and make drawings of all you hare ob- 

 served. 



36 



