40 
TACTILE ORGANS OF BLIND FISH. 
smooth, but on either side is provided with numerous transverse 
and longitudinal ridges (PL 1, fig. 7), which are, on the whole, 
regularly arranged. The first row of transverse ridges, eight or 
nine in number, begins between the nostrils and extends back- 
wards, diverging from the median line. The third ridge is crossed 
at its outer end by a longitudinal one, as are also two others farther 
back. The second and third rows, situated, in part, on the sides 
and, in part, on the under surface, are less regular than the preced- 
ing. A fourth, oil the borders of the operculum, is still less well 
defined. The transverse are also crossed here by longitudinal 
ridges. About ten vertical ridges, also provided with papillae, and 
similar to those on the head, are visible on the sides extending from 
the pectoral fins to the tail, but are not so well defined as those on 
the head. The skin of the head is of extreme delicacy and is cov- 
ered by a very thin, loose layer of epitheliiim.” — Wyman. 
“The larger ridges have between twenty and thirty papillae, 
many of these having a cup-shaped indentation at the top, in 
which a delicate filament is, in some instances, seen (PL 1, fig. 9). 
These papillae are largely provided with nervous filaments, and, as 
is obvious from their connection with branches of the fifth pair of 
nerves, must be considered purely tactile, and the large number of 
them shows that tactile sensibilitj^ is probably very acute and in 
some measure compensates for the virtual absence of the sense of 
sight. Plate 1, fig. 8, represents one of the ridges of the bead 
magnified, showing the papillae of which it is made up, and figure 
9 shows three papillae still more enlarged. Two of these show a 
cup-shaped cavity at the top, and the short, slender filament al- 
ready mentioned. The surface of the papillae is covered with 
loosely connected epithelium cells. Fig. 10 shows the nervous fil- 
aments distributed to the papillae : «, a branch of the fifth pair of 
nerves passing beneath the papillary ridge and sending filaments 
to each papilla. These papillary branches interchange filaments, 
forming a nervous plexus in connection with each ridge. This 
figure of the nerves was drawn with a camera lucida, from a speci- 
men treated with acetic acid.” — Wyman. 
“Plate 1, fig. 6, represents a double S 3 ’stem of subcutaneous ca- 
nals, which extend the whole length of the head, but were not 
traced farther back than the edge of the naked or scaleless skin 
which covers it. Forwards they bifurcate, nearly encircling the 
nasal cavity, towards the middle line ending in a blind pouch. 
