THE TURBELLARIA. 



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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 Turhellaria which resemble Macrostomum in having 

 a straight, simple digestive cavity, are termed Hhabdocoela, 

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

 capable of being protruded from, or retracted into a chamber 



Pia. S2.—Oi)isthomum (after Schulzo).— a, central nervous system ; ramifications of 

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

 deferentia; /, vesicuia seminalis; g, pouis ; h, sexual aperture; i, vas^ina ; 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. 33, c). 



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

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