THE ANCESTHY OF VERTEBRATES 



291 



greatly increases. The l^ody now shows (Fig. 27G) two open- 

 ings; one inhalent (o), and one exhalent {at). Some species, 



-ARVACEA > 



-^ ~d ^ ^^ 



Asc d id=; 



Mclgulids 



CyntTi ds 



JCcmipound 

 \Ascidians 



Fig. 274. — A group of Tunicates shomng the attached forms (Ascidiacea) 

 both .simple (left-hand side of picture) and compound (at right) ; the 

 oceanic form,s (Thaliacea) that swim near the surface ; and the small tailed 

 forms (Larvacea) that look like the larval stages of higher Tunioata. From 

 Cambridge Natural History. 



after becoming attached, form colonies by budding new zooids 

 upon the side of their body. The whole colony may have a 

 common exhalent opening (Fig. 277, d). 



Below the tunicates is a small group of worm-like animals 



