PHYLUM PLATYHELMINTHES 



iS3 



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 flame-cell. The flame- 

 cell (Fig. ioo) 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 of Planaria. c, cilia ; 

 place to place, lies principally in three sets e ; ope " in K g , int0 ™ CTe - 



" r sr r- j tory tubule. (From 



of muscles: a circular layer just beneath Lankester's Treatise.) 

 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 



