THE ANIMAL KINGDOM 



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Fig. 228. — Types of Turbellarians. (Based on von Graff.) A and B, Rhabdo- 

 coeles; C, triclad; D, polyclad. The alimentary canal is represented in solid 

 black. B shows strobilation or division taking place in a chain of four individ- 

 uals of Microstomum. Division begins in the alimentary canal by the formation 

 of septa which reach to the body wall. The chain really consists of sixteen 

 partially formed zooids. b, bursa copulatrix; g, genital aperture; m, mouth; n, 

 nervous system; o, ovary; p, penis; r, receptaculum seminis; s, vesicula seminalis; 

 t, testis; u, uterus; v, vagina; y, yolk glands; in C and D, the testis and its ducts 

 are shown on the left side of the animal and the ovary and oviduct on the right. 



