PLATVHELMINTHES 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 
off numerous minute side branches, each of which ends in 
a flame 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 
Fic. 59.—Plan of a Rhabdocoelous 
Turbellarian. Von Graff. 
. Bursa copulatrix. 
hor oe 
. Brain. 
Hye. 
. Germarium. 
. Intestine. 
. Longitudinal nerve trunk. 
. Mouth. 
. Pharynx. 
oOo onrr nr OP OO 
. Receptaculum seminis. 
— 
So 
. Salivary glands. 
11. Testis. 
12. Uterus, containing an egg. 
13. Yolk gland. 
14. Vesicula seminis. 
g. Chitinous copulatory organs. 
6%. 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 in the parenchyma. From each 
corner a strong nerve is given off. The anterior nerves run to 
