i8 



HYDROIDS, ETC. 



These jellies are disk-shaped, the tentacles in Cya- 

 nea hanging in eight distinct bunches from the margin, 

 and armed with darts or lasso-cells, that form terrible 



FIG. 16. Adult Aurelia, showing the water-vascular canals. 



weapons of defense. Around the fringed margin are 

 eight protected eyes. The mouth - opening is square, 

 leading into a large stomach, from which radiate four 

 branching tubes (Fig. 16) called water-vascular canals. 



They form a network at the 

 edge, and connect with a tube 

 that encircles the margin of 

 the disk. Through these 

 branches digested food and 

 water circulates, or finds its 

 way over the body. A some- 

 what similar arrangement is 

 found in all jelly-fishes. In 

 swimming, the disk contracts 



and expands in regular time, 

 FIG. 17. Development of Au- v 



reiia. i. Early stage. 2. averaging twelve or fifteen times 



Jelly-fish ready to break off. a minute. 



