40 TACTILE ORGANS OF BLIND FISH. 



smooth, but on either side is provided with numerous transverse 

 and longitudinal ridges (PI. 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, on the borders of the operculum, is still less Avell 

 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 epithelium." 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 sensibility 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, 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 w T ith 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 system 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. 



