162 
BULLETIN OP THE BUREAU OF FISHERIES 
Fig. 30. — Anterior third of a longitudinal section of a specimen taken 
on the day it hatched. Length, 8 millimeters. The digestive tract 
appears as an almost solid cord of cells passing over the heart chamber 
and descending to the ventrally located oral depression 
were found in the mouth of a specimen of this size. At the lips the epithelium is 
continued as the integumentary epidermis, which is five to six polygonal cells in thick- 
ness, the outermost, however, being a con inuous layer of flatter cells. Taste buds are 
found here also, but are broader and 
do not pass beyond the surface. A 
small fold of the epithelium of the 
mouth (breathing valve) is seen 
just inside the upper lip. It bears 
no taste buds. 
At 16 millimeters the oral mu- 
cosa is from 8 to 10 cells thick, but 
as the cells are of similar rounded 
form stratification is not evident. 
This epithelium has doubled in 
thickness — 40 microns — the papillse 
still rising 20 microns above the sur- 
face. A section 10 microns in thick- 
ness shows as many as 15 of these 
sense papillse surmounting a single 
branchial arch (cut transversely to the arch), and as many as 40 of them per milli- 
meter in a line along the roof of the pharynx. (Fig. 32.) 
Just a little way back of the upper lip and breathing valve is another cluster of 
large taste buds. The epidermis of the integument has developed numerous goblet 
mucus cells and the mesoderm is 
entering into the formation of the 
lips. The taste buds inside the 
mouth all project above the sur- 
face of the epithelium, those of 
the lips projecting slightly as low, 
rounded elevations. In the skin 
they do not project and none 
occurs on the breathing valve. 
At 42 millimeters the epithe- 
lial portion of the oral mucous 
membrane is 80 microns in thick- 
ness; that of the skin is 100 mi- 
crons. So numerous are the taste 
buds on the lips that, as in the 
pharynx, they frequently touch 
one another. This is the condi- 
tion after the mouth has become 
inferior, and probably differs lit- 
tle from conditions later in the 
life of the fish. In a specimen 65 millimeters long the lips are papillose in the 
sense of having macroscopic elevations. Each of these, on sectioning, is found to 
contain a battery of the microscopic taste buds (called “sense papillse'’ above). 
Fig. 31.— Longitudinal section of head of an 11-millimeter specimen. 
The early high terminal position of the mouth opening is seen clearly 
here 
