206 CCELENTERATA 



Summary of Important Facts. 



1. The sponge body is largely a mass of connective tissue covered 

 externally with pavement epithelium (mesectoderm) and penetrated by 

 canals. 



2. An entoderm of collared flagellate cells occurs only in the ampullae 

 or flagellate chambers which are intercalated between incurrent and ex- 

 current canals (in ascons in the central cavity). 



3. The animals receive food through fine pores in the body wall; 

 indigestible matter is cast out through one or more oscula. 



4. Since nerves, muscles, and sense organs are lacking or very weakly 

 developed, only inconspicuous movements occur. 



5. Sponges are divided into Calcispongue and Silicispongiae according 

 to the character of the skeleton. 



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PHYLUM III. CCELENTERATA (CNIDARIA). 



The ccelenterates, formerly called Zoophyta (plant-animals), were 

 united by Cuvier with the Echinoderma to form the type Radiata, a union 

 which Leuckart, the father of the name Ccelenterata, set aside because 

 separate intestinal and body cavities occur in the Echinoderma, while in 

 the Ccelenterata' there is but a single cavity in the body. Each name 

 indicates certain important characters of the group. 



(1) The name Zoophyta referred to the general appearance. Most 

 ccelenterates, like plants, are fixed and by incomplete budding form bush- 

 like or mossy colonies. This resemblance is but superficial, for there is 

 not the slightest doubt of the animal nature of any ccelenterate. The 

 name therefore does not imply that these are doubtful forms on the border 

 between plants and animals. Besides, there are free-moving forms which 

 swim with great ease. 



(2) Most Coelenterata are radially symmetrical. There is a main 

 body axis, one end of which passes through the mouth and the other 

 through the blind end of the digestive tract, and the organs of the body are 

 radially arranged around this so that the body may be divided into 

 symmetrical halves by numerous planes. In the higher Ccelenterata this 

 may be replaced by a biradial symmetry or even by bilaterality (Cteno- 

 phora, many Anthozoa). 



(3) The term Coelenterata is given because these animals contain a 

 single continuous ca'lenteron or gastrovascular cavity. In its simplest 

 form this is a wide-mouthed sac into which food passes for digestion. 

 The single opening into it serves for both mouth and anus; the sac itself is 

 the alimentary tract. Frequently lateral diverticula or branched canals 



