XIII 



PHYLUM CHORDATA 



29 



FIG. 729. Colony of Pyrosoma. A, side view ; B, end- 

 view. (After Herdman.) 



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 bril- 

 liantly phosphorescent. 

 The enteric canal 

 in Appendicularia (Fig. 

 723) consists, in addi- 

 tion to the pharynx, of 

 a narrow oesophagus, a 

 bilobed stomach, and a 

 straight intestine (int.) 

 which opens directly 

 by an anal aperture 

 (an.) situated on the 

 ventral side. The 

 alimentary canal of 

 the simple Ascidians 

 has already been de- 

 scribed, and there are 

 few differences of con- 

 sequence in the various 

 families, except that in 

 some cases there is a well-developed digestive gland or "liver"; 



in the composite forms 

 jfg#\ j>roc 



1 



the arrangement of the 

 parts as the same in all 

 essential respects as in 

 the simple. In the Salpse 

 and in Doliolum and 

 Octacnemus the aliment- 

 ary canal forms a rela- 

 tively small dark mass 

 the so-called nucleus 

 towards the posterior end 

 of the body; it consists 

 of oesophagus, stomach, 

 and intestine, the anal 

 aperture being situated 

 in the peribranchial or 

 atrial part of the internal 

 cavity. 



The heart in all has 

 the simple structure al- 

 ready described in the 

 simple Ascidian. In Ap- 

 pendicularia its wall 



IG. 730. Part of a section through a Pyrosoma 

 colony, atr. up. atrial aperture ; or. ap. oral aper- 

 ture ; proc. processes of test on outer surface of 

 colony ; ph. pharynx ; stol. stolon on which are de- 

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

 (After Herdman.) 



