THE TURBELLARIA. 



159 



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

 male aperture being posterior to the female. The margins of 

 the male aperture are produced into a curved prominence, the 

 penis. 



Those Turbellaria which resemble Macrostomum in having 

 a straight, simple digestive cavity, are termed Mhabdoccela. 

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

 capable of being protruded from, or retracted into a chamber 



6&» a A 



> : &\ 



;m« 



M: 



:4m 



m 



Fig. 32.—Opisthomum (after Schulze). — a, central nervous system ; ramifications of 

 the water-vessels are seen close to it; b, mouth; c, proboscis; d, testes; e, vasa 

 deferentia; /, vesicula seminalis; g, penis ; A, sexual aperture; i, vagina ; k, sper- 

 matheca ; I, germarium ; m, viteliarium ; n, uterus with two ova inclosed within 

 their hard shells. 



formed by the walls of the circum-oral region of the body 

 (Fig. 32, c). 



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



