XIII 



PHYLUM CHORD ATA 



25 



Octacnemus, allied to Salpa, appears to be fixed, and has the 

 oral and atrial aper- A 



tures towards one end 

 of the body, which is 

 somewhat discoid, with 

 its margin 

 into eight 



B 



FIG. 686. Colony of Pyrosoma. A, side view ; B, end 

 view. (After Herdmaii.) 



produced 

 tapering 



processes. 



Pyrosoma (Fig. 686) 



is a colonial Tunicate, 



the colonies of which 



are of a cylindrical 



form, with an orifice 



at one end and usually 



closed at the other. 



The oral apertures (Fig. 



687, or. ap.) of the 



zooids are situated on 



the outer surface of 



the cylinder on the 



extremities of a series 



of papillae. The colonies 



of Pyrosoma, which may 



be from two or three inches to four feet in length, are pelagic. 



and are brilliantly phos- 

 phorescent. 



The enteric canal in 

 Appendicularia (Fig. 680) 

 consists, in addition to the 

 pharynx, of a narrow reso- 

 phagus,a bilobed stomach, 

 and a straight intestine 

 (int.) which opens directly 

 by an anal aperture (an.) 

 situated on the ventral 

 side. In Oikopleura the 

 intestine is absent. The 

 alimentary canal of the 

 simple Ascidians has al- 

 ready been described, and 

 there are few differences 

 of consequence in the 

 various families ; in the 



FIG. 687.-Part of a section through a Pyrosoma Composite forms the ar- 



colony. air. ap. atrial aperture ; or. ap. oral aper- rangement of the parts IS 



ture ; p'toc. processes of test on outer surface of , ' . ,, . , 



colony ; ph. pharynx ; stol. stolon on which are de- the Same in all CSSential 



veloped buds giving rise to new zooids ; tent, tentacles. r^-norta a in th P <si m nl P 



[(After Herdman.) respects as in me siinpie. 



lent 



stol 



