CHAP, x.] DIGESTIVE APPARATUS IN THE ANIMAL SERIES. 1C1 



in common : in the compound ascidia 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 proceed* 

 on the internal surface of the intestine, where we remark a 

 coverin of coloured cells. 



Fio. 7. FIG. 8. 



FIG. 7. Astericus vemumlftius, open at the dorsal face, a, anus; i, stomach expanded in 



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

 FIG. 8. Digestive organs of a spider, ee, oesophagus ; c, superior cesophagian ganglion, 



cerebroidal ; v, stomach ; V, lateral prolongations ; v", appendices directed upwards ; i, 



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



into the intestine ; e, urinary canals. 



The asteroids, properly so called are without anus, and have 

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

 furnished with caecal appendices extending by pairs in each 

 radius. (Fig. 7.) 



