METRIDIUM. 35 



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, 

 cinclides, 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 coelenteric chamber. 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 

 secretory organs that are probably equivalent to the gastric 

 filaments of the Scyphozoa. 



3. Quite near the bases of the mesenteries are the attachments 

 of the acontia. What relation have they to the mesenteric fila- 

 ments? 



4. Also located on the mesenteries, and arranged parallel 

 to the filaments, but back from the edge a bit, are the repro- 

 ductive organs or gonads. Are they found on all of the mesen- 

 teries? The ova or spermatozoa are shed into the coelenteric 

 chamber and pass out through the mouth. 



Cut one of the halves of your specimen transversely in the 

 region of the esophagus, and study the arrangements of the 

 mesenteries, their attachments, etc. 



5. How many pairs of primary mesenteries, i. e., those attached 

 both to the outer body-wall and to the esophagus, are there? 

 The directive septa are those at the angles of the esophageal tube. 

 The portion of the coelenteric cavity between any two pairs 

 of mesenteries is termed an inter-radial chamber. The space 

 between the two mesenteries of each pair is called an intra- 

 radial chamber. 



