PLA TYHELMINTHES 



85 



forward and one running backward on each side of the body. 

 These branches give off the very numerous secondary ducts 

 which ramify all over the body. The secondary branches give 

 ofp numerous minute side branches, each of which ends in 

 a ilame cell. The flame cells are pear-shaped cells, the stalk 

 being formed by a flagellum which projects into the lumen of 

 the minute duct. The body of the cell is often branched ; it 

 contains a large nucleus, and a vacuole which is continuous 

 with the lumen of the duct. The fluid contained in the 

 excretory system is clear and free from corpuscles, it is kept 

 in motion by the flagella of the flame cells. 



The nervous system consists of a central organ, the brain, 

 and certain nerves running from it. The brain is somewhat 



10-, 



FiQ. 59. — Plan of a Ehabdocoelous 

 Turbellarian. Von Graff. 



1. Bursa copulatrix. 



2. Brain. 



3. Eye. 



4. Germarium. 



5. Intestine. 



6. Longitudinal nerve trunk. 



7. Mouth. 



8. Pharynx. 



9. Beceptaculum seminis. 



10. Salivary glands. 



11. Testis. 



12. Uterus, containing an egg. 



13. Yolk gland. 



' 14. Vesicula seminis. 



(J . Chitinous copulatory organs. 

 (J 9. Common sexual aperture. 



oblong in shape, and separated into two halves by a slight fur- 

 row. It is situated between the pharynx and the anterior end 

 of the animal, and is embedded iu the parenchyma. From each 

 corner a strong nerve is given off. The anterior nerves run to 



