METRIDIUM. 41 



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? Mount living acontia under a cover-slip in sea-water 

 and notice the central muscle strand, nematocysts, and cilia. 



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. 



6. Carefully determine the disposition of the longitudinal 

 retractor muscles on the mesenteries. Do they occupy similar 

 positions on all of the mesenteries? 



7. Examine the upper parts of the mesenteries for openings, 

 septal stomata, that put the chambers in communication 



8. Are the tentacles solid or hollow? 



Make a drawing of a longitudinal section and another of a 

 cross-section. Put into these all of the points of the anatomy you 

 have seen. 



If time and opportunity permit, it is very desirable that this 

 form should be compared with specimens of the order Madre- 

 poraria, and later with the Alcyonaria. Such a form as Astran- 

 gia may easily be obtained either alive or properly preserved, 

 and will serve to show the relation of the hard parts of the coral 



