Chap, x.] DIGESTIVE APPARATUS IN THE ANIMAL SERIES. 161 



in common : in the eomponnd asuidia there is likewise a cloaca in 

 common where meet all the anus of the colony. 



Differentiation takes a sufficiently important step forward in 

 the bryozoaries and the tunicates. The elaboration of the 

 aliments has in them become more complex by the existence of 

 glandular sacs though these are still isolated and rudimentary. 



In a certain group of echinoderms the progress continues. 

 Sometimes the buccal edges, hardened, play the part of masti- 

 catory apparatus : sometimes (echinoids) there are complicated 

 apparatus of mastication. Besides a special secretion proceeds 

 on the internal surface of the intestine, where w;e remark a 

 covering of coloiu-ed cells. 



Fin. 7. Fig. 8. 



Fig, 7. — Astericus vernw.'nlfi(«?, open at the dorsal face; a, anus; i,. stomach expaBded in 



form of rosette ; h, radiating and tubular appendices of the intestine ; g, genital glands, 

 Fio. 8. — Digestive organs of a spider, os, (esophagus ; c, superior cesophagian ganglion, 



cerebroidal ; u, stomach ; w', lateral proloogations ;. r", appendices directed upwards ; i, 



median intestine ; r, intestinal extremity enlarged into oloaCa ; hh' openings of the liver 



into the intestine ; e, urinary canals. 



The asietciids, properly so called are without anus, aaid have 

 a stomach stellated like their body. The stomach is in effect- 

 furnished with caecal appendices extending by pairs in each 

 radius. (Kg. 7.) 



M 



