PHYLUM PLATYHELMINTHES 



153 



EXCRETORY SYSTEM. - - The excretory system comprises 

 a pair of longitudinal, much-coiled tubes, one on each side of the 

 body; these are connected near the anterior end by a transverse 

 tube, and open to the exterior by two small pores on the dorsal 

 surface. The longitudinal and transverse 

 trunks give off numerous finer tubes which 

 ramify through all parts of the body, 

 usually ending in a ilame-cell. The flame- 

 cell (Fig. 100) is large and hollow, with a 

 bunch of flickering cilia (c) extending into 

 the central cavity (e). Since it communi- 

 cates only with the excretory tubules, it is 

 considered excretory in function, though it 

 may also carry on respiratory activities. 



MUSCULAR SYSTEM. - - The power of 

 changing the shape of its body, which may 

 be observed when Planaria moves from 

 place to place, lies principally in three sets 

 of muscles: a circular layer just beneath 

 the ectoderm, external and internal layers 

 of longitudinal muscle fibers, and a set of oblique fibers lying 

 in the mesoderm. 



NERVOUS SYSTEM. - - Planaria possesses a well-developed 

 nervous system consisting of a bilobed mass of tissue just be- 

 neath the eye-spots called the brain (Fig. 99, en), and two lat- 

 eral longitudinal nerve-cords (In) connected by transverse nerves. 

 From the brain, nerves pass to various parts of the anterior 

 end of the body, imparting to this region a highly sensitive 

 nature. 



REPRODUCTIVE SYSTEM. - - Reproduction is by fission or by 

 the sexual method. Each individual possesses both male and 

 female organs, i.e. is hermaphroditic. The male organs may be 

 located easily in Figure 99; they consist of numerous spherical 

 testes (t) connected by small tubes called vasa deferentia (vd); 

 the vas deferens from each side of the body joins the cirrus or 



FIG. ioo. Flame-cell 

 of Planaria. c, cilia ; 

 r, opening into excre- 

 tory tubule. (From 

 Lankester's Treatise.) 



