172 



UNSEGMENTED ' ' IVOR MS. ' 



Order 2. Tricladida. Elongated flat " Planarians " with 

 three main branches from the gut, e.g. Planaria and 

 Dcndroca'luni (fresh water), the former sometimes dividing 

 transversely ; Gunda segmentata (marine), showing hints of 

 internal segmentation ; Geodestmis and Bipaliwn (in damp 



FiG. 82. Diagrammatic figure 

 of a simple Turbellarian. 



in., Mouth ;//z., pharynx ;g-., digestive 

 part of gut ; I.e., longitudinal excre- 

 tory vessels; e.p., excretory pore; 

 Ect., ciliated ectoderm ; Ms., meso- 

 clerm ; End., endoderm. 



FIG. 83. Diagrammatic figure of 

 part of the structure of a simple 

 Turbellarian. 



Ect., Ciliated ectoderm ; e.g., cerebral 

 ganglion; /.., lateral nerve; 7\, 

 testes ; oi'., ovary. 



earth) ; Bipalhnu keivciise is an import often found in 



Britain. 

 Order 3. Polycladida. Large leaf-like marine (( Planarians," 



with numerous intestinal branches diverging from a central 



stomach, e.g. Leptoplaua (not uncommon on the seashore), 



Thysanozoon. 

 Class Temnocephaloidea. Flattened forms, e.g. Teninocepliala, 



found clinging to fresh-water animals, especially Crustaceans ; 



there is a large ventral sucker ; the epidermis is a nucleated 



