458 SUB-PHYLUM UROCHORDA OR TUNICATA. 
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 larve 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 Lancelcts 
(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 aiose from a common stock of primitive chordate 
animals 
