THE DEVELOPMENT OF AMPHIOXUS 



45 



(Fig. 9, C), opening upon the surface of the left side of the 

 head, in front of the mouth. When the rudimentary folds of 

 the oral hood appear, the dorsal fold develops just above the 

 opening of the preoral pit, which thereafter remains as a struc- 





vt 



FIG. 16. Ventral view of anterior end of adult Amphioxus. The buccal 

 cavity has been cut open along the mid- ventral line and spread out. After 

 Goodrich, b, Buccal skeleton; ch, notochord; cr, cirri; gH, groove of Hatschek; 

 h, oral hood, Hn, Hatschek's nephridium; mi, ms, first and third myotomes; 

 n, nerve coming from left side; o, pharyngeal opening of Hatschek's nephridium. 

 ro, Raderorgan; s, solenocytes; v, velum; vt, velar tentacles. 



ture chiefly related with the buccal cavity. Early in the larval 

 period the preoral pit enlarges and then divides into a dorsal 

 and a ventral portion. The ventral or stomodceal portion, as it 

 is called, enlarges very considerably, moves to the surface, and 



