Some of the Lower Metasoans 395 



help in locating food, and one statocyst which contains small calcareous 

 materials for aid in orienting the animal. 



In the center of the subumbrella surface is the mouth which is 

 at the end of the very short manubrium. Surrounding the mouth are 

 four long, grooved oral lobes which contain nematocysts along their 

 edges. From the mouth, a short gullet leads into the "stomach," Lead- 

 ing from the stomach are four gastric pouches within which are located 

 the gonads and a row of small gastric filaments bearing nematocysts. 

 Leading from the pouches are many small radial canals which connect 

 with the marginal ring canal. 



The four oral lobes and the four gastric pouches are located on the 

 same plane which is termed the perradii; halfway between each two of 

 these four points are the interradii along which are located the septa. 

 The eight special sense organs are located along the ends of these four 

 interradii and four perradii. 



The sexes are separate in most members of the Scyphozoa. After 

 fertilization, the eggs usually develop to the planula stage in small 

 pouches in the fringes of the oral arms. The planula is released and 

 swims about before settling down and becoming a small polyp, the 

 scyphistonia. This divides by transverse fission into a series of small 

 jellyfish. Before these separate, the whole small structure is known 

 as a strohila. When the young jellyfish are ready to separate, they are 

 constricted o^ by muscular contractions and swim free as the ephyra 

 stage. An ephyra has eight arms, each with a terminal bifid portion, 

 the two lappets. By expansion and growth, the area between the arm 

 fills in and the adult medusa results. 



THE CLASS ANTHOZOA 



The members of the class Anthozoa are all marine and occur only 

 as polyp forms. Many of them are flowerlike in appearance and ex- 

 tremely handsome. The class includes such forms as the corals, sea 

 anemones, sea pens, and sea pansies. In some respects, their structure 

 is considerably advanced over that of the other two classes of this 

 phylum. The symmetry rather than being radial is biradial ; also the 

 mesoglea has been penetrated to such an extent by cells that a good 

 mesoderm is produced. 



Although the members of this class are quite varied, most of the 

 anatomical features are illustrated by the members of the genus Metrid- 

 tmn, one of the common sea anemones. 



