Ill 



PL A TODESGASTRO-CANAL SYSTEM 



141 



the free end of the pharynx is directed forwards and is extended forwards. The 

 opposite is the case when the mouth lies behind the middle of the body. The 

 generally narrow round enteric aperture leads out of the pharynx or pharyngeal 

 pouch into the endodermal gastral system. 



II. The endodermal g-astral system must be separately described 

 for the various divisions of the Platodes. 



An anus is everywhere wanting, as in the Cnidaria. 



FIG. 103. Intestinal and nervous systems of the Planocera. t, Tentacle; g, brain; ph, 

 pharynx ; o, mouth ; hd, posterior end of the main intestine, the greater part of which is covered 

 by the pharynx. 



Turbellaria. 



A. Polyelada (Fig. 103). The gastral system here is very 

 similar to that of the higher Cnidaria (Medusa and Ctenophora}. It 

 consists of (1) the main intestine and (2) the gastro-canals or intestinal 

 branches. The longer the body the longer is the generally spacious 

 main or stomach intestine. Where the pharyngeal apparatus is 

 found in the middle of the body, the main intestine lies just above 

 it ; where the pharynx lies behind, the intestine in almost every case is 

 found in front of it. If the pharynx is placed in front the main intestine 

 lies nearly always behind it. From the stomach intestine the gastro- 

 canals arise in varying numbers. They perforate the body parenchyma, 

 penetrating towards the edge of the body in a horizontal direction on 

 all sides, and freely branching or anastomosing with each other on the 

 way. Pairs of gastro-canals can lie distinguished, and there is one 

 unpaired canal. The paired are found in 4 pairs at least, and often, 



