176 ZOOLOGY 



do you find in the mesenteries? They are described as complete (or 

 primary), and incomplete (or secondary, tertiary, etc.). 

 Show by a diagram the number and arrangement of them, especially of the 

 primary. Are they in pairs? Notice the inter-mesenteric chambers. 

 Can you find the muscular thickenings in the cut mesenteries? Sketch 

 their position. Compare with conditions figured in various text-books. 



3. Longitudinal Section. 



Complete your study of the structures mentioned above. 



Compare the complete and incomplete mesenteries. 



Identify: 



Mesenteric filaments (on free edge of mesenteries). 



Genital glands (developed in the substance of the mesentery near the edge). 



Ostia, or ring canal; openings through the mesenteries by means of which 



the mesenterial chambers communicate with one another. 

 Are the tentacles solid or hollow? 



4. General Considerations. 



Make diagrams in longitudinal and transverse view to show the distribution 

 and connection of the cavities of the body. Is the mouth the only opening into 

 the cavity? Describe the symmetry of the anemone. Is it radial or bilateral? 

 Give reasons for your answer. 



220. Oculina (or other branching coral). Study the branches and note the 

 position of the polyps. Is the arrangement orderly? If so, describe. 



Note with a hand lens the arrangement of the septa, which grow between the 

 fleshy mesenteries of the coral. Compare their arrangement with that of the 

 mesenteries of anemone. 



DESCRIPTIVE TEXT 



221. Some authors place the sponges and the ccelenterates 

 in the same group on account of the typical barrel shape, the 

 absence of a true ccelom or body cavity, the somewhat similar 

 character and origin of the middle mass (mesenchyma) , and 

 the agreement of the principal axis of the adult with that of the 

 gastrula. In the ccelenterates however there are no lateral 

 pores. The principal opening serves as a real mouth as well 

 as vent for the voiding of undigested matter, whereas in sponges 

 it is not a mouth in any sense. In general the individual, even 

 in the colonial forms of ccelenterates, is more distinctly an in- 

 dividual than in the sponges. The division of labor among the 

 parts and the interdependence of parts is greater than among the 

 sponges. 



222. General Characters. 



i. A single system of internal chambers (gastro-vascular 



