36 CCELENTERATA. 



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 Orbicella, 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 ccelenteric 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 

 how the polyps are placed. The structure of the expanded 

 polyps is nicely shown by Renilla. The spicules of such forms 

 as Gorgonia may be obtained by boiling a portion of a colony 

 in caustic potash. What purpose do such spicules serve? 



Parker: The Reactions of Metridium to Food and Other Substances. 

 Bui. Mus. Comp. Zool. Harvard, 29, 1896. 



: The Mesenteries and Siphonoglyphes in Metridium marginatum. 



Bui. Mus. Comp. Zool., Harvard, 30, 1897. 



: Longitudinal Fission in Metridium marginatum. Bui. Mus. Comp. 



Zool., Harvard, 35, 1899. 



: The Reversal of the Effective Stroke of the Labial Cilia of Sea- 

 Anemones by Organic Substances. Am. Jour. Physiol., 14, 1905. 



