METRIDIUM 43 



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, \. 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 cha7nber. 



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 

 to the polyp. You should understand the relation of the septa 

 and the mesenteries, and of the polyps to each other. If speci- 

 mens are at hand, compare such forms as Orhicella, Favia, and 

 Meandrina, or any forms that show gradations from separate 

 calices to fused groups, and understand the positions of mouths, 

 the arrangement of the coelenteric chambers, and the way in 

 which the colony has come to its present form. You should 

 also examine large branching colonies and determine why branches 

 are formed and how they arise. 



Examine the structure of an Alcyonarian colony and see 



