2GG CiELENTERATA 



Summary of Important Facts. 



1. The sponge bodv is largely a. mass of connecti\e tissue covered 

 externally with pavement epithelium (nieseetoderm) and penetrated by 

 canals. 



2. An entoderm of collared llagellate cells occurs only in the ampulla? 

 or tlagellate chambers wliich arc intercalated between incurrent and ex- 

 current canals (in ascons in the central cavity). 



V The animals recei\'e food through line 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 Calcispongia- and Silicispongi;c according 

 to the character of the skeleton. 



PHYLU^I III. CCELEXTERATA (CNIDARIA). 



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

 united hv Cuvier \yith the Echinoderma to form the type Radiata, a union 

 wliich Leuckart, the father of the name Cadenterata, set asitle because 

 separate intestinal and liody cavities occur in the Ecliinodcrma, wliile in 

 the Calenterata there is but a single ca\ity in the body. Each name 

 indicates certain important characters of the group. 



(i) The name Zoophyta referred to the general appearance. INIost 

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

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

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

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

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

 swim with great ease. 



(2) INIost Ccelenterata are radially symmetrical. There is a main 

 bodv a.xis, one end of wdiich passes through the mouth and the other 

 tlirough 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 Ctvlcnicrata tlris 

 may be replaced i)y a biradial s}'mmetry or e\en by bilaterality (Cteno- 

 phora, many .\nthoz<ia). 



(3) The term r(clenterata is gi\-cn iiecause these animals contain a 

 single continuous civlcnlcnm or ;^astrovasctdar ca\ity. 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 



