FLATWORMS AND THREADWORMS 



Each of these flame-cells (which are characteristic of the flatworms) 

 consists of a central cavity into which a bundle of cilia project. The 

 flickering of the cilia look something like a candle-flame, and it is from 

 this fact they are named. It is the flame-cell which is considered the 



real excretory organ of the animal, though 

 some writers think it may also have some 

 respiratory functions. 



The Nervous System. 



There are two lobes (Fig. 176) of nerv- 

 ous tissue beneath the eye-spots. These are 

 usually called the brain. There are also two 

 longitudinal nerve-cords, one on each side 



Fig. 176. Anatomy of a Flatworiu. 

 en, brain ; e, eye ; g, ovary ; i v i 2 , iy 

 branches of intestine ; In, lateral nerve ; m, 

 mouth ; od, oviduct ; ph, pharynx ; t, testis ; 

 u, uterus ; v, yolk glands ; vd, vas deferens ; 

 <j" , penis ; ? , vagina ; c? , ? , common genital 

 pore. (From Lankester's Treatise, after v. 

 Graff). 



Fig. 177. 

 c, cilia ; e, 



Flame-cell of Planaria. 

 opening into the excretory 



tubule. (From Lankester's Treatise). 



of the body, connected by transverse nerves. Nerve branches pass into 

 the head proper from the brain region, so that the anterior end becomes 

 the more sensitive. 



The Muscular System. 



Immediately beneath the ectoderm, a group of muscles form a 

 dermo-muscular sac around the internal organs. There are two layers, 

 an inner longitudinal and an outer circular. 



The Reproductive System. 



Planaria are hermaphroditic, having both male and female repro- 

 ductive organs (Fig. 176). These animals nevertheless often reproduce 

 by fission. Each animal has numerous spherical testes which are con- 

 nected by small tubules called vasa deferentia. The single vas deferens 

 from each side of the body empties into, or through, the cirrus into the 

 genital cloaca. 



At the base of the cirrus there is a seminal vesicle and several uni- 

 cellular prostate glands. 



