30 CCELENTERATA. 



ACTINOZOA. 



METRIDIUM. (Sea- Anemone.) 



Specimens are quite common on piles, as well as on rocky 

 bottoms, and may be easily observed by means of a glass- 

 bottomed pail. Most of the observations can be made much 

 better on specimens in aquaria, but it is desirable to see their 

 natural surroundings. 



1. Notice the shape and attachment of expanded, living speci- 

 mens in an aquarium, or in a deep finger-boAvl. The free end, 

 called the disk or 'peristome, is fringed with tentacles, and the 

 elongated mouth is located in the middle of this area. At one 

 or both angles of the mouth the lips are thickened into what is 

 called a siphonoglyph. 



Make a drawing of the animal. 



2. Feed a specimen with bits of mashed clam to ascertain 

 its manner of taking in food. Drop bits on the tentacles at one 

 time, and disk at another. 



Endeavor also to determine whether there are currents 

 constantly passing in or out of the mouth that are due to ciliary 

 action. 



3. Irritate the animal and observe its manner of contraction. 

 When fully contracted, if the irritation is continued, thread- 

 like structures, acontia, are thrust out through minute pores, 

 cinclidcs, in the body-wall. 



Make a drawing of the contracted animal. 



Internal Anatomy. — Using preserved material, place the edge 

 of a razor across the peristomial area, at right angles to the 

 mouth-slit, and divide the animal from disk to base into halves. 



1. Note the extent of the esophagus and siphonoglyphes; 

 they lead into the ca:lenteric chamhcr. Find the extent of this 

 chamber, and the method of its subdivision by delicate parti- 

 tions, the mesenteries, or septa. Are all of the mesenteries alike ? 



2. Forming the free edges of the mesenteries, below the 

 esophagus, are the convoluted mesenteric filaments, which are 



