COELENTERATA 



63 



Nervous System and Sense Organs. — The nervous system consists 

 of a plexus of nerve fibers extending over the subumbrellar surface 

 between the epithelial layer of ectoderm and the muscular layer. 

 The plexus is thickened in a ring extending around the animal near 

 the circular canal and connecting with the sense organs, or tentaculo- 

 cysts. The marginal tentaculocysts are equilibratory and olfacto- 

 gustatory. Adjacent to the ocellus or statocyst are found the so- 

 called " olfactory pits." 



Fig. 26. Development oi Aurelia. First row, growth of planula to scyphostoma; 

 below, strobilation (separation of ephyrae): left, oral view of scyphostoma; right, two 

 ephyrae. (After Hertwig-Kingsley, Manual oj Zoology, after Hatschek. Courtesy of 

 Henry Holt & Co.) 



Class 3. Actinozoa (Anthozoa). Sea Anemone. — The Actino- 

 zoa include numerous species of sea anemones and corals. Sea 

 anemones are solitary animals, forming no permanent colony. 

 They are fleshy, with no skeleton. 



Anatomy of the Sea Anemone. — The sea anemone is cylindrical, 

 with xx.^ peristome covered with hollow, horn-shaped tentacles, bear- 

 ing nematocysts. The mouth is provided with a muscular ciliated 

 groove, the siphonoglyph, which aids in holding and propelling the 

 food. George Meredith said, " Sea anemones are flowering stomachs 

 which open to anything and speedily cast out what they cannot con- 



