Coelenterata. 323 



and sperms, which develop into polyp form. The siphon- 

 ophores are in colonies, but, instead of being fixed, are 

 free. Some swim by means of bell-shaped zooids, resem- 

 bling a cluster of medusae, while other zooids in the group 

 devote themselves to nutrition, and others to the work of 

 protection. In other kinds of siphonophores there is a 

 bladderlike float, and locomotion depends upon the wind 

 and current. The Portuguese man-of-war is an example. 

 All forms are well provided with stinging cells, and one 

 who handles them carelessly finds that this whole branch 

 may well be designated "the sea nettles." 



CLASS II. THE SCYPHOZOA. 



Jellyfishes. This class is mostly made up of the larger 

 jellyfishes. One of the most common on the New Eng- 

 land coast is the common white jellyfish, known as Aurelia. 

 It is saucer-shaped and frequently is a foot or more in 

 diameter. It is gelatinous and semitransparenf. In the 

 center of the subumbrella is a short stalk, or manubrium. 

 At the end of this is the square mouth, from the corners 

 of which extend four delicate processes, the oral arms. 

 The short gullet leads from the mouth to a roomy stomach, 

 whose four gastric pouches extend halfway to the margin. 

 There are many fine radiating canals and a small, circular 

 marginal canal. On the floor of each gastric pouch is a 

 brightly colored gonad, whose contents, eggs or sperms, 

 are discharged into the stomach and pass out through the 

 mouth. Along the inner border of each gonad is a row 

 of delicate gastric filaments, well supplied with stinging 

 cells, whose function is to paralyze the animals taken in as 

 food. The margin has a fine fringe of tentacles. Evenly 

 distributed on the margin are eight peculiar sense organs. 



