370 Animal Biology 



Circulation. — There is 7io special circulatory system, but the branched 

 intestine serves as a gastrovascular cavity in which foods, wastes, water, 

 etc., circulate. 



Respiration. — Respiration takes place through the general body sur- 

 face as well as through the surface of the intestine (gastrovascular 

 cavity) . 



Excretion and Egestion. — Wastes are eliminated from the intestine 

 through the mouth. Coiled excretory tubes run lengthwise along the 



Eye spot 



Auricle 



Brain 



~Zz.-\-^^ '^^^^<^ cords 



r^rr^r^ =.- Transverse nerves 



Fig. 178.— Nervous system of Dugesia (Planaria). Observe the nerves leading 



from the brain to the auricle. 



two sides of the body and are connected near the anterior end by a 

 transverse tube. This system opens exteriorly through small excretory 

 pores on the dorsal surface behind the eye spots. Additional openings 

 along the excretory tubes may exist. The small lateral branches of the 

 tubes divide, redivide, and terminate in a large, hollow, flame cell. The 

 latter contains a bunch of motile cilia to propel wastes. The motile cilia 

 tend to flicker like a flame; hence, "flame cell" (Fig. 177). 



