106 Trans. Acad. Sci. of St. Louis. 



the dorsal enlargement of the main nasal sac from the 

 lateral diverticulum in which the nasolacrimal duct ends. 

 The latter is supported by a little process of cartilage 

 which grows forward from the Lamina cribrosa and turns ven- 

 trad toward the trabecular horn. 



The cartilaginous nasal skeleton of Stage IV. is far from 

 completion ; dorsally the nasal organ is only partly covered 

 by the Lamina cribrosa and the edge of the medial nasal pro- 

 cess ; the future anterior and posterior cupolas are only sug- 

 gested by these processes of cartilage which are inclining in 

 their growth toward the antorbital process and the trabecular 

 horn respectively. 



The conditions present in the ethmoidal region of a 39mm. 

 larva of Ambly stoma jeffersonianum have been described by 

 Winslow. The nasal capsule of my Stage IV seems to be 

 less advanced. 



Stage V. 



Ambly stoma of 40-45 mm. Gills partly atrophied. 



The nasal sac is in front of the brain except for its caudal 

 one-third; the olfactory foramen looks more forward than 

 outward. 



The nasal capsule is provided with a broad, continuous roof 

 extending over nearly the whole dorsal aspect of the main-sac. 

 Its caudal part is the Lamina cribrosa ; its cephalic part the 

 medial nasal process which now reaches beyond the external 

 naris and forms the anterior cupola. Between these parts is 

 a broad bay within which are the external naris and the 

 cephalic end of the nasolacrimal duct. This bay becomes 

 the Fenestra narina (Gaupp '05. 2, foot-note, p. 280). 



The ventral edge of the medial nasal process turns under 

 the main-sac a little way and is still separated from the trabe- 

 cular horn by the now widely extended medial incisure. The 

 extreme lateral end of the process is, however, very near the 

 trabecular horn. The latter sends dorso-caudad a cylindrical 

 process the end of which is connected by precartilage with 

 the tip of the little cartilaginous support afforded the nasolac- 



