XIII 



PHYLUM CHORDATA 



17 



tent 



leal 



Ir.v 



manl 



of the two ventral longitudinal folds with the groove between 

 them, the term endostyle (end.]^ is applied. The cells covering the 

 endostyle are large 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 dis- 

 charging a viscid mucous matter. Anteriorly the endostyle is 

 continuous with 

 a ciliated ridge 

 which runs cir- 

 cularly round 

 the anterior end 

 of the pharynx. 

 In front of this 

 circular ridge, 

 and running 

 parallel with it, 

 separated from 

 it only by a 

 narrow groove, 

 is another ridge 

 of similar char- 

 acter : these are 

 termed the 

 periphary ngeal 

 ridges; the 

 groove between 

 them is the 

 periphary ngeal 

 groove. Dor- 

 sally, i.e. oppo- 

 site the endo- 

 style, the pos- 

 terior peri- 

 pharyngeal 

 ridge passes 

 into a median, 

 m u c Ji 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. In the 

 living animal the lamina is capable of being bent to one side in 

 such a way as to form a deep groove. The mucus secreted by 

 the gland-cells of the endostyle forms viscid threads which entangle 

 food-particles (microscopic organisms of various kinds) ; the cilia 

 VOL. u c 



vLsc.br 



slot 



FIG. 727. Ascidia, diagram of longitudinal section from the left 

 side, the test and mantle removed, an. anus ; air. cav. atrial 

 cavity ; air. siph. atrial siphon ; br. car. branchio-cardiac vessel ; 

 card. vise, cardio-visceral vessel ; dors. v. dorsal vessel ; gonod. 

 gonoduct ; ht. heart ; hyp. neural gland ; mant. mantle ; ne. gn. 

 nerve-ganglion ; oes. oesophagus ; or. siph. oral siphon ; ov. ovary ; 

 reel, rectum ; stigm. stigmata ; stow, stomach ; tent, tentacles ; test, 

 test ; tr. v. transverse vessel ; vent. v. ventral vessel ; vise. br. 

 viscero-branchial vessel. (From Herdman, after Perrier.) 



