72 INVERTEBRATE ZOOLOGY 



formed opens into the genital cloaca. This structure, which thus 

 receives all the ducts from the genital glands, communicates 

 with the outside through the genital pore, a median, ventral 

 opening in the hinder part of the body. 



Exercise 3. Draw a large outline of the animal and place in it as 

 much of the reproductive system as you have observed. 



The nervous system. Beneath the eye-spots will be seen the 

 opaque brain, a large nervous mass consisting of a pair of minor 

 masses united by a broad commissure. From its anterior and 

 lateral sides numerous sensory nerves pass to the anterior body- 

 surface, which render this extremity a highly sensitive tactile 

 organ. From its posterior side a pair of large longitudinal nerve 

 cords passes to the hinder end of the body, being united at 

 intervals by transverse nerves. 



The excretory system. This consists of a system of minute 

 tubes which extend throughout the body and collect the excrete 

 matters from the tissues. There are two main longitudinal tubes 

 extending the length of the body, which open to the outside 

 through minute pores on the dorsal surface of the animal. 

 These tubes are not straight but coiled and give off numerous 

 branches, at the termination of each of which is a peculiar cell 

 with a vibratory process at its base called a flame cell ; they are 

 joined by a transverse tube at the anterior end of the animal. 

 Portions of the excretory system can often be seen in the com- 

 pressed animal, where they appear as fine lines. 



Exercise 4. Draw an outline of the animal and place in it as 

 much of the nervous and the excretory system as you 

 have observed. 



No special respiratory system is present in the Turbellaria, 

 the ciliated outer surface of the body performing this function. 

 A circulatory system and a blood fluid are also wanting. The 

 branching of the digestive and excretory systems is correlated 



