ASCIDIACEA FIXATION AND METAMORPHOSIS. 375 



\ d ft I 



FIG. 173. Diagram illustrating the metamorphosis of the larva of Clavelina during 

 and after fixation (mainly after SEELIGER). A, free-swimming larva ; J5, larva just 

 attached ; C, older metamorphosed stage, ch, chorda ; e, atrial aperture ; ed, in- 

 testine ; ep, epicardial process; es, endostyle;/, ectodermal fold ; /Z, ciliated pit; 

 g, ganglion ; h, heart ; hp, adhering papillae ; i, branchial aperture ; ks, gill-slits ; 

 p, atrial cavity ; r, trunk-portion of the medullary tube ; *, partition-wall of the 

 stolon ; sb, sensory vesicle ; ss, the cast cellulose envelope of the tail ; st, stolo pro- 

 lifer ; x, the larval tail in course of degeneration. 



