62 



COELENTERATA 



and with the aid of the nematocysts on the jnarginal tentacles^ to 

 kill it preparatory to digestion. From the mouth leads a short 

 gullet, situated on the 7nanubrium. The stomach is extended at 

 four points into the horseshoe-shaped gastric pouches. These have 

 relatively thick jelly walls. The gastric pouches have many gastric 



filaments^ covered with nem- 

 atocysts, so that even if prey 

 remains alive up to that point, 

 it can be killed. 



The radial canals carrying 

 food to the circular canal are 

 of two types, the unbranched 

 adradial, which proceed di- 

 rectly from the sides of the 

 gastric pouches to the circular 

 canal, and which have no 

 sense organs at their ends; and 

 the branched canals, called 

 per-radial and inter-radial. 

 The per-radial canals orig- 

 inate at the corners of the 



Fig. 25. Aurelia, a Scyphozon. (From 

 Verrill.) 



mouth, between the pouches, and have a sense organ at the end 

 of their central trunk; the inter-radial canals branch so close 

 to the gastric pouches that one cannot in some cases actually see 

 the beginning of the lateral branching. They arise at the middle 

 of the outer margin of the gastric pouches, and they also have sense 

 organs at the end of the main trunk. 



Respiration is osmotic through the entire animal; and possibly 

 facilitated by means of the subgenital pit. Circulation is not 

 vascular, merely by water currents with food in suspension. Ex- 

 cretion is by the extrusion of solids through the mouth, and by 

 osmosis. Again the subgenital pits may function. The circular 

 canal of some medusae communicates with the exterior by small 

 excretory pores at the tips of papillae. These apparently function 

 in the excretion of nitrogenous wastes. 



Reproduction. — The gonads are situated in the gastric pouches 

 and the eggs or sperms are discharged, not through the subgenital 

 pits, but into the stomach and out through the mouth. Fertilized 

 eggs are frequently seen developing attached to the oral arms. 

 (Figure 26.) 



