I4S 



DEVELOFMEXT OF AMFHIOXL'S. 



The priEoral pit itself is absorbed, as it were, into the 

 oral hood, so that it eventually loses its independent exist- 

 ence as a pit, althotigh the sense-organ of the praeoral pit 

 persists in the adult as a deep groove in the dorsal wall 

 of the oral hood to the right of the base of the notochord. 

 The remaining ciliated epithelium of the original prxoral 

 pit increases in extent, and grows out into the finger- 

 shaped tracts which we have alread\" described as being- 

 characteristic of the inner surface of the oral hood, consti- 

 tuting the so-called " Riiderogan." (Cf. Fig. 3.) 



Equalisat!i.vi of the Gill-slits. 



In the stage next succeeding that of which a ventral 

 view is gi\-en in Fig. So. the first eight primarv slits — that 

 is to sav, from the ori£:inal second to the ninth inclusive — 



Fig. S4. — L.irv.i toward the c'ose of the metamorphosis, from the left side. 

 (.\fter \\"ILLEY.1 



c'. Olfactorv- pit. ;.\-e'.um. /..'. Peripharyngeal b.ind. i-. Endostv'.e. ;*..;-. Second 

 primary sHt. the first having closed up. ;-;. Left meiap'.eur. ,.-..;. Floor of atrium. 

 /.-'"!-. /..'I'J. \-estiges of the twelfth and thirteenth prim.irv slits. 



have become definitely established on the left side, their 

 longitudinal and vertical a.xes are equalised, and in most 

 of them the tongue-bars are completelv formed ^Fio-. s_j.). 

 No tongue-bar is formed in the first slit on either side, and 

 this slit apparently remains as a rule simple throughout 

 life. 



