THE TURBELLARIA, I59 



externally by a median pore on the oral face of the bodv, the 

 male aperture being posterior to the female. The margins of 

 the male aperture are produced into a curved prominence, the 

 penis. 



Those Tiirhellaria which resemble Macrostomwn in having 

 a straight, simple digestive cavity, are termed Rhahdociiela. 

 They, for the most part, possess a buccal proboscis, which is 

 capable of being protruded from, or retracted into a chamber 



M 



Fig. Zl.—Oplsthomum (after Schulze).— (7, contral nervous system; ramifications of 

 tlie water-vessels are seen rlose to it; b. mouth; c, proboscis; d. testes; e, vasa 

 deferentia; /, vesicula seminalis; q, piMiis ; h, sexual aperture; i. va<4-ina ; k. sncr- 

 matheca; /. i,'ermarium; m, viteliiiriuui ; n, uterus witli two ova inclosed within 

 their hard shells. 



formed bv the vralls of the circum-oral region of the body 

 (Fig. 32, c). 



In some (e. g., Prostomum) the anterior end of the body is 



