XII 



PHYLUM CHORDATA 



A 



321 



&r 



FIG. 201. Diagram of the metamorphosis of the free, tailed larva into the fixed 

 Ascidian. A, stage of free-swimming larva; B, larva recently fixed; C, older 

 fixed stage, adk, adhesive papillae; atr, atrial cavity; cil.gr, ciliated groove; 

 end, endostyle; ht, heart; med, ganglion of trunk; n. gn, nerve-ganglion; noto, 

 notochord; or, oral aperture; rect, rectum; sens ves, sense vesicle; stfg, stig- 

 mata; stol, stolon; t, tail. (From Korschelt and Heider, after Seeliger.) 



