PLA TYHELMINTHES 



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The Platyhelminthes are hermajphrodite ; in the female 

 organs a vitellarmm is often found. Reproduction may he 

 asexual at times, and then an alternation of generations 

 takes place. 



Class I. TUKBELLARIA. 



Chaeacteeistics. — Free - living Platyhelminthes, whose oval, 

 v^vMly flattened hody is covered with cilia. A mouth, a 

 muscular pharynx, and an alimentary canal exist, but no 

 anus. No special respiratory system or vascular system, or 

 hooks, are present. Nervous system, a paired cerebral 

 ganglion and two lateral nerve cords. With few exceptions 

 hermaphrodite. 

 The Turbellaria are mostly aquatic, inhabiting the sea 



and fresh water, but a few live on the earth amongst damp 



■ ■ ?•* a*- 



Fig. 55. — Various forms of Turtellaria, 

 all natural size, and viewed from the 

 dorsal surface. After Von Graff. 



a. Convoluta paradoxa, Oe. 

 6. Vortex vi/ridis, M. Seh. 



c. Monotus fvscus, Gff. 



d. Thysanozoon brocchii, Gr., with ele- 



vated anterior extremity (after 

 Joh. Schmidt). 



e. Rhyncodemus terrestris, 0. F. Miiller 



(after Kennel). 

 /. Bipalium ceres, Mos. (after Moseley). 

 g. Polycelis cornuta, 0. Sch., attached 



by the pharynx (ph) to a dead 



worm (after Johnson). 



surroundings (Fig. 55); a very few are parasitic, and then 

 occur in MoUusca or Holothurians. Several are common in 

 ditches and standing water in England; Planaria lactea, a 

 Dendrocoel, especially so. One of the Ehabdocoela, which 



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