60 J. B. Johnston. 
whole oro-pharyngeal cavity, meets the ectoderm about midway on 
the anterior and posterior surfaces of the branchial arches in the 
gill slits and meets the ectoderm in front of the maxillary and 
mandibular teeth at the lips. 
7. Formation of Taste Buds. 
The taste buds begin to be formed shortly before the mouth cleft 
forms. They appear eventually, more or less numerous, on all parts 
of the floor and roof of the oro-pharyngeal cavity forward to, but not 
in front of, the maxillary and mandibular teeth. The buds appear 
d.mand. 
Fic. 18. <A. punctatum, stage when the teeth are forming. Median sagittal 
section of mouth region to show forward projection of entoderm between 
maxillary and vomerine teeth through which the connection of nasal and oral 
cavities is formed. Iron hematoxylin, fuchsin. é 
first in the pharynx and later farther forward, as I found to be the 
case in teleosts (1905). In the larval stage of Petromyzon they are 
found in the pharynx only. The buds in the greater part of the roof 
of the mouth and pharynx and those in a large part of the floor are 
formed in entoderm far removed from any ectoderm. There is, and 
can be, no question as to their origin from entoderm. ‘The buds 
which are formed on the gill arches are always on the inner surface, 
and there is no reason to doubt that they are formed from entoderm 
cells as are those in the roof of the pharynx far removed from the 
ectoderm. The buds which are formed in the vicinity of the teeth 
are the ones which one might think would be derived from the in- 
