JO 



DEGENERA TION. 



the other of these apertures. If we remove the 



« 



leathery outer-case (Fig. 15), we find that there is 

 a soft creature within which has the following 

 parts : — Leading from the mouth a great throat, fol- 

 lowed by an intestine. The throat is perforated by 

 innumerable slits, through which the water passes 



Fig. 14.— a colony of compound Ascidians (Botryllus) growing on a piece of sea- 

 weed (Fucus). Each star corresponds to eight or more conjoined Ascidians. 

 Natural size. 



into a chamber — the cloaca : in passing, the water 

 aerates the blood which circulates in the framework 

 of the slits. The intestine takes a sharp bend, 

 which causes it to open also into the cloaca. Be- 

 tween the orifice of the mouth and of the cloaca 

 there is a nerve-ganglion. 



