458 SUB- PHYLUM UROCHORDA OR TUNIC AT A. 



there are two possible views as to the position of Appendicularia and 

 its allies. They may be regarded as the slightly modified descendants 

 of the primitive Tunicates, from which the Ascidians have diverged in 

 the direction of degeneration, or as prematurely sexual larvae derived 

 from an already degraded Ascidian-like form. Both views have had 

 supporters, and the one adopted materially affects the general method 

 of regarding the group. 



In any case the Larvacea retain persistently a number of characters 

 which were probably possessed by the primitive Tunicata. 



There are several resemblances between Tunicates and Lancelets 

 (see the next chapter), e.g. the relatively large respiratory pharynx and 

 the peribranchial cavity, but this probably does not mean more than 

 that both groups arose from a common stock of primitive chordate 

 animals 



