452 
HENRY F. NACHTRIEB 
account and figures are based upon recently made preparations 
that I believe present conclusive and irrefutable evidence against 
the generally accepted view that the primitive pores are distinc- 
tive sense organs. 
My best material was obtained from the living fish, fresh from 
the water. Pieces of the bill, operculum and other parts of the 
head were immediately placed into various hardening fluids. 
Since the fish has little vitality out of the water in the summer, 
and the epithelium at this time of the year sloughs off very easily 
shortly after the death of the fish, prompt hardening of the ma- 
terial is important. Various hardening fluids, such as formalin, 
formol-corrosive sublimate-acetic acid, trichloracetic acid, Zenker 
and Gilson fluids were used. Small pieces of the hardened ma- 
terial were imbedded in paraffin, cut into series of sections, three, 
four, five, seven and ten microns thick, fixed to the slide, variously 
stained and finally mounted in xylol damar. Some pieces were 
stained in toto and yielded good general results. The connective 
tissue is apt to become very tough during the processes of harden- 
ing and imbedding. It is therefore advisable to limit the material 
to be cut to the epithelium as far as possible. Sections stained 
with Heidenhain's iron hematoxylin yielded the clearest positive 
results and, unless specifically stated otherwise, the following 
descriptions are based on sections stained by this method. Sec- 
tions stained with other aqueous, and alcoholic stains, present 
the same general characters, though not always with the same 
distinctness. 
In sections parallel to the long axis of the primitive pore the 
epithelium of the bottom of the pit is clearly and sharply marked 
off from the epithelium lining the rest of the pit. While the 
epithelium on the floor of the pit is the immediate bone of con- 
tention, it is necessary to consider briefly the skin epithelium be- 
tween the pores and to examine carefully its relation to that of the 
pore, especially to that lining the floor of the pit. 
Just beyond the mouth of the primitive pore the skin epithe- 
lium may be ten to fifteen or more cells deep. The outer or sur- 
face cells are thin plates. The basal cells are more or less slender 
columnar cells. In some regions the basal cells are very long and 
