TUNICATA 



595 



the branchial basket work to the mantle. Its median dorsal part is 

 known as the cloaca, the parts at the sides of the branchial chamber as 

 the peribranchial cavities. One important difference between this 

 atrium and that of Amphioxus should be noted. The atrium of the 

 Cephalochorda is ventral: that of the Tunicata is dorsal. 



By the apparatus just described the animal feeds. The working of 

 the cilia at the sides of the stigmata drives water through the latter, 

 from the pharynx to the atrium, whence it passes out by the atrial 

 opening as the current which has already been mentioned. This 

 results in water being drawn in through the mouth to replenish the 

 pharynx. Mucus secreted by the gland cells of the endostyle is by the 

 cilia of that organ passed on to the inner face of the branchial basket 



Fig. 446. A diagram of a transverse section of Ciona, with an enlarged view 

 of the endostyle. The thick arrows show the course of the main current, the 

 thin arrows that of the food particles, at. atrium; ci., ci.' short and long 

 cilia; est. endostyle; gl. gland cells; lang. languet. 



work, over which by further ciliary action it is passed to the dorsal 

 languets. These receive it with their curved ends, slung in which it is 

 worked backwards as a rope to the oesophagus. As it passes over the 

 pharyngeal wall particles brought in with the current through the 

 mouth are entangled in it, to be carried to the hinder part of the 

 alimentary canal and there digested if they be fit for food. A similar 

 function is performed by mucus which passes dorsalwards along the 

 peripharyngeal band. 



The short oesophagus leads backwards to a fusiform stomach. From 

 this an intestine, whose ventral wall projects inwards as the typhlo- 

 sole does on the dorsal side of the intestine of the earthworm, loops 

 forwards to become the rectum, which runs a straight course half-way 

 along the atrium, lying near the dorsal side of the pharynx. The 



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