TURBELLARIA. 



163 



B. Dendroccelida. Larger, flatter forms with branched intestine. 



( i ) Tricladida. Elongated flat " Planarians " ; the mouth 

 and tubular pharynx lie behind the middle of the body ; 

 intestine with three main branches, themselves branched ; 

 two ovaries, numerous yolk glands and testes, a common 

 genital aperture., e.g., Planaria and Dendroccelum (in 

 fresh water), the former sometimes divides transversely; 

 Gunda segmentata (marine) showing hints of internal 

 segmentation ; Geodesmus and Bipalium (in damp earth). 



c. F . 



FIG. 50. Diagrammatic figure 

 of a simple Turbellarian. 



m, Mouth ; ph, pharynx ; f, digestive 

 part of gut ; l.e, longitudinal excre- 

 tory vessels ; e.p, excretory pore ; 

 Ect, ciliated Ectoderm ; Ms, meso- 

 derm ; End, endoderm. 



FIG. 51. Diagrammatic expres- 

 sion of part of the structure of 

 a simple Turbellarian. 



Ect, Ciliated ectoderm ; c.g; cerebra 

 ganglion ; /., lateral nerve ; T, 

 testes ; ov, ovary. 



(2) Polycladida. Large leaf - like marine "Planarians," 

 with numerous intestinal branches diverging from a central 

 stomach ; with numerous ovaries and testes, without yolk 

 glands, mostly with two genital apertures. 



e.g., Cycloporus (showing beginning of anus), Leptoplana, 

 Thysanozoon. 



