FLATWORMS. Organs that have an undoubted excretory function are first met with in the flat worms (Platyhelminthesl. They are known as the water-vascular system. This system consists, in Planaria, of two lateral coiled tninks, one on the right and one on the left side of the body, from which many side branches ramify through the tissues of the body. These tubes open on the dorsal su•faee of the body by means of several minute pores. The fine lateral branches sub divide so as to give rise to still finer capillary vessels. Each of these latter may terminate in a flame-cell. The flame-eell is nucleated, and contains a vacuole or space in communication with a capillary. The vacuole contains one or more vibratile cilia. whose flickering motion. like that of a candle-flame, has given rise to the term flame-cell. A respiratory function has also been maintained for this system. The excretory sys
tem of the liver-fluke consists of one main trunk, which terminates anteriorly in four large, branch ing trunks. The latter eventually lead into flame cells. Posteriorly the main trunk ends in an ex cretory pore. In the tapeworm there are four longitudinal water-tubes, which extend through out the entire length of the Worn. At the pos terior end of each proglottis they are connected by a transverse tube. At the posterior end there is a pulsating caudal vesicle which opens to the exterior. As in the planarian, so in the tape worm the main trunk gives rise to dendritic branches which end in flame-cells. The lateral tubes of nematodes and rotifers end in a com mon duct or a contractile vessel, respectively, posteriorly, and in flame-cells at the other end.