XVII 



PKOTOCHOEDATA 



621 



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FIG. 452. Anterior portion of 

 free-swimming tadpole of 

 the simple Ascidian Phal- 

 lusia maiiii/iillata, seen from 

 above. (After Kowalevsky. ) 



u, position where anus \vill In- 

 formed ; at, atrial involutions ; 

 6.y, brain-vesicle ; emlxt, i-ndosl \ l^ ; 

 fx, fixing processes ; i/.<i, ygi, the 

 first two gill-slits ; /'/, intestine; 

 in, mouth; inn, t-hin (mental pro- 

 cess); ms, longitudinal muscles nt 

 the tail; n.t, nerve tube; oc, eye- 

 cup; fit, otolith ; /ill. phai-ynx. 



