i8o 



ELEMENTARY ZOOLOGY. 



and one-half feet in diameter. Most species, however, are much 

 smaller, ranging from one-fourth inch to two or three inches. 



The mouth is in the middle of the free end of the animal. When 

 food is taken into the mouth it does not pass at once into the gastro- 

 vascular cavity. It enters an oesophagus or gullet lined with ectoderm 

 (Fig. sO- This gullet opens below into a central cavity which 



B 



ab. o. 



FIG. 51. Diagram of sea-anemone. A, cross section ; B, longitudinal section. 

 Lettering as in Fig. 50. c, chamber between the mesenteries (m). 



Questions on the Figure. How does the symmetry of this animal 

 compare with that of the jelly-fish? Compare these with figures in 

 reference books showing the whole animal. Trace the extent and 

 divisions of the gastro-vascular cavity. Identify mouth, gullet, 

 tentacles, mesenteries (primary and secondary), ectoderm, entoderm, 

 and mesoderm. What is there about the structure of this animal 

 that seems to adjust it to its mode of life? 



extends outward to the body wall. It is partially divided up, 

 however, by a series of flat radial partitions (Figs. 51, mes.), some of 

 which run from the body wall to the gullet. The whole cavity is 

 lined with entoderm. Food may pass out into any of these chambers 

 between the partitions, from the central cavity just below the gullet. 



