XIII 



PHYLUM CHORDATA 



25 



B 



FIG. 086. Colony of Pyrosoma. A, side view ; B, end 

 view. (After Herdnian.) 



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 produced 



into eight 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 oeso- 

 phagus^ 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 COlllpOSlte lOrillS the ar- 



colony. atr. ap. atrial aperture ; or. ap. oral aper- ran^ement of the Darts is 

 ture ; pioc. processes of test on outer surface of . . 



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

 veloped buds giving rise to new zooids ; tent, tentacles. , v i 



(After Herdman.) respects as in the simple. 



proc 



tent 



stol 



