io6 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



the Metazoa, any secretion poured out into the gastric 

 cavity from the cells which line this space, but a 

 number of the cells would appear to retain the power 

 of separately assimilating the food material. Obser- 

 vation of these endoderinal gastric cells shows that they 

 vary considerably in size according to the fasting or 

 well-fed condition of the animal ; and we are entitled 

 to suppose that these cells become smaller after the 

 process of digestion, in consequence of their having 

 given up part of their acquired material to the other 

 cells of the body ; cells which, be it understood, have 



lost the power 

 of independently 

 assimilating nu- 

 triment. We 

 have here to do 

 with nutrient 

 cells, just as in 

 the Ccelenterata 

 (page 39) we ob- 

 served nut rien t 

 persons (trophos- 

 omes)ina colony. 

 A history, 

 not unlike that 

 of Hydra, may 

 be told of a 

 Sponge; but 

 here, it is interes- 



Fig. 53. Flagellated Chambers (c) of Turkey , . , 



tm g to note , we 



have to do not 



with an amce b o id 



ingestive cell, 

 but with another form which, no less, has its representa- 

 tive among the Protozoa ; we find, that is, a " collared- 

 cell" taking the place of the amoeboid cell (Fig. 53). In 

 the "ciliated "or "flagellated "chambers which are found 



Bath Sponge, showin? the collared-cells and 



flageiium. 



K, Excurrent canal s ^ Current canals. (After 



