XIII 



PHYLUM CHORDATA 



15 



cells of two kinds ciliated cells and gland cells the former beset 

 at their free ends with cilia, the action of which is to drive floating 

 particles that come within their influence outwards towards the 

 oral aperture, the latter secreting and discharging a viscid mucous 

 matter. Anteriorly the endostyle is continuous with a ciliated 

 ridge which runs circularly round the anterior end of the pharynx. 



tent 



test 



Ir.v 



mant 



ve.nl. v 



slam. 



FIG. 676. Ascidia, diagram of longitudinal section from the left-hand side, the test and mantle 

 removed, atr. cav. atrial cavity ; atr. siph. atrial siphon ; br. car. branchio-cardiac vessel ; 

 card. vise, cardio-visceral vessel ; gonod. gonoduct ; ht. heart ; hyp. hypophysis ; mant. mantle ; 

 n. gn. nerve-ganglion ; oes. oesophagus ; ov. ovary ; rect. rectum ; stiff, stigmata ; stom. stomach ; 

 tent, tentacles ; test, testis ; tr. v. transverse vessel ; vent. v. ventral vessel ; vise. br. viscero- 

 branchial vessel. (After Herdman.) 



In front of this circular ridge, and running parallel with it, sepa- 

 rated from it only by a narrow groove, is another ridge of similar 

 character ; these are termed the peri-pharyngeal ridges ; the groove 

 between them is the peri-pharyngeal groove. Dorsally, i.e. opposite 

 the endostyle, the posterior peripharyngeal ridge passes into a 

 median, much more prominent, longitudinal ridge, the dorsal lamina 

 (dors, lam.), which runs along the middle of the dorsal surface of the 

 pharynx to the opening of the oesophagus. The mucus secreted by 



