PLATYHELMINTHES 203 



The excretory system lies in the parenchyma. It con- 

 sists of a meshwork of tubules joining into a 

 system.'" 1 ' mam duct which lies in the middle line, from a 

 point about a quarter of the length of the body 

 behind its front end to the excretory pore at the hind end. 

 The ultimate branches of the tubules are very fine and end 

 in little structures known as flame cells. These are minute 

 vesicles containing a few long cilia which keep up a flicker- 

 ing movement like that of a flame and drive towards the 



Fig. 123. — Two flame cells, highly magnified. 



main duct the fluid secreted into the vesicle by its walls. 

 Each vesicle has a nucleus and may be regarded as a hollow 

 cell. It is connected with its fellows by fine protoplasmic 

 processes which are said to be hollow. 



The nervous system consists of a collar around the 



pharynx with a mid-ventral swelling and a 

 system! P air of latera l swellings. From these swellings 



or ganglia nerves are given off to the forepart 

 of the body, and from each lateral ganglion arises a large 

 lateral nerve cord which runs backwards below the gut to 

 the hinder end of the body, giving off branches on the way. 



14 



