TUNICATA 673 



end. Anteriorly, the same strips are continuous with the posterior 

 peripharyngeal ridge, on each side of a gap in the latter. Dorsally, 

 the lateral walls are separated by a hyperpharyngeal band, from which 

 there hangs down into the branchial cavity a row of processes, the 

 languets, which are curved to one side. 



The stigmata lead, not directly to the exterior, but into a cavity, 

 the atrium, which opens externally at the atrial opening, is lined by 

 ectoderm, and is placed dorsally like a saddle upon the branchial 

 chamber, surrounding the latter completely except {a) in front, and 

 {b) in the median line ventrally, posteriorly, and for a short distance 

 from the front end dorsally. The atrium is crossed by vascular trabe- 

 cule from the branchial basket work to the mantle. Its median dorsal 



Fig. 471. 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. 



part is known as the cloaca, the parts at the sides of the branchial 

 chamber as the peribranchial cavities. One important difference be- 

 tween this atrium and that of Atnphioxus 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 re- 

 sults 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 

 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 



