XIII 



PHYLUM CHOTiDATA 



29 



B 



Fi<;. 7-20.- 



Colony of Pyrosoma. A, sMu view ; B, cnd- 

 vicw. (After Hcrdiiuui.) 



a series of papill;^. The colonies of Pyrosonin, whirh may be fi-om 



two (jr three inches to a 



i'oiir feet in U/no-th, ai'e 



pelagic, and are hiil- 



liantly })hiisphorcsccnt. 

 The enteric canal 



in Appen(hcularia (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 

 the arrangement of the 

 parts is the same in all 

 essential respects as in 

 the simple. In the Salpas 

 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 



stoL 



atr^ctp 



10. 730. — Part of a section through a Pyrosoma 

 colony, atr. up. atrial aperture ; or. <ip. 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.) 



