174 Practical Zoology. 



The cavity of the body is divided into a series of radial com- 

 partments by fleshy vertical partitions, the mesenteries, which ex- 

 tend inward from the body wall, some reaching the esophagus and 

 being attached to it, others not extending so far inward as the 

 esophagus. Each tentacle communicates with one of these radial 

 compartments, and is to be regarded as a mere extension of part 

 of the body cavity. 



Alcoholic specimens should be sliced transversely and longi- 

 tudinally. In a transverse section of the lower part of the body 

 there will be seen the body wall with a series of partitions ex- 

 tending inward and ending in a free edge. The section across 

 the upper part of the body shows an outer circle, the body wall, 

 an inner circle, the stomach wall, and, connecting the two, the 

 radially arranged partitions, or mesenteries. Like the hydroids, 

 the sea anemone is well provided with thread cells. 



Food is taken into the mouth, digested in the stomach, then 

 passed, mixed with sea water, into the body cavity, through which 

 it is made to circulate by the contractions of the body walls. The 

 indigestible portions of the food are expelled from the stomach 

 through the mouth. 



STONY CORALS. 

 (Coral Proper.} 



In a piece of stony coral, or compound skeleton of a colony of 

 coral polyps (Galaxea is a good form to study), make out the 

 following points : 



1 . The nature of the material itself ; test by putting a very 

 small piece into weak acid, or by touching the specimen with a 

 drop of acid. 



2. The cup, or theca, formed by an individual polyp, often 

 traceable as a long tube. Observe : 



a. The outer wall of the cup. 



b. The partitions, or septa, extending inward from the wall of 

 the cup. 



3. Between the cups, the porous limy secretion, which was 



