TEE BPONi 



15 



- .mo Infusoriana also andergo :i process common 

 m low plants, called "conjugation."* 



younc 



m 



mi 



Fiq. 18. — .1. Epistylia flavicana Ehr., a single, many-forked colony of bi 

 malcules, slightly magnified. B, one of the animalcules a 

 ■ ■it- rs ;•. the stem; • /, the flal spiral of vibrating cilia at the edge of 



the muscle; m t" o, the depth of the diges • the mouth; y, y 1 , 



the thr atractile vesicle; n, the rep g ^u. 



( EAPTEB II. 

 Branch 1 1. Porif] ra (S •>• 



General Characters of Sponges. Sponges are i 

 ah to be composed of numerous c< I s, arrai gred in three 

 layers, the embryo arising from an egg, and p through 



a blastula and a gastrula , as in all the higher an in 



A sponge, then, i.- a cellular sac (Fig. L3) with dig 

 chambers or minute rude stomachs lined with ciliated nils, 

 the whole sponge-mass being propped up by an irregular 

 basket-work of needle-like bodies called spicules. Upon 

 cutting a dry sponge in half 1 - inals 



which have large openings called oscula : these art- really 



* See Kent's .Manual of ibe Infusoria, Luudo: 



