XIII 



PHYLUM CHORDATA 



21 



of the mouth. This leads into a tolerably wide pharynx (Fig. 

 680, ph.), in the ventral wall of which is an endostyle similar to 

 that of the simple 

 Ascidian, but com- 

 paratively short. 

 Round the pharynx 

 there run two bands 

 covered with strong 



FIG. 079. Appendicularia (Oikopleura) in 



(From Herdmau, after Fol.) 



House." 



or.ap 



geal bands. On the 

 ventral side of the 

 pharynx there are 

 two ciliated openings 

 -the stigmata (stig.) 

 - which communi- 

 cate with the exterior by short passages the at Hal canals, 

 situated on either side behind the anus. The axis of the tail is 

 occupied by a cylindrical rod the notochord (noto.). 



A remarkable peculiarity of Appendicularia is the power which 

 it possesses of secreting from the surface a transparent envelope 

 (Fig. 679) in the interior of which the animal can move freely. 

 This structure the house as it is called is soon thrown off, and 

 a new one developed in its stead. It represents the test or 



tunie of the simple 

 Ascidian, though it 

 does not appear to 

 contain cellulose. 



Among the simple 

 Ascidians there is a 

 considerable degree 

 of uniformity of struc- 

 ture, and there is not 

 much that need be 

 added here to the ac- 

 count given of the 

 example. The shape 

 varies a good deal : it 

 is sometimes cylindri- 

 cal, sometimes globu- 

 lar, sometimes com- 

 pressed ; usually 

 sessile and attached 

 by a broad base, often 

 with root-like processes, but in other cases (e.g. Boltenia) elevated 

 on a longer or shorter stalk. Most are solitary ; but some multiply 

 by budding, stolons being given off on which new zooids are 

 developed. The test varies considerably in consistency, being some- 



ruito 



FIG. 680. Diagram of Appendicularia from the right- 

 hand side. an. anus ; ht. heart ; int. intestine ; ne. nerve ; 

 ne.' caudal portion of nerve ; ne. gn. principal nerve- 

 ganglion ; ne.gn.'ne. gn." first two ganglia of nerve of 

 tail ; iioto. notochord ; cts. oesophagus ; or. up. oral aper- 

 ture ; oto. otocyst ; peri. Id. peripharyngeal band ; ph. 

 pharynx ; Us. testis ; stig. one of the stigmata ; stoin. 

 stomach. (After Herdman.) 



