t 
586 The Sensory Organs. _ [September, 
in the mucous canals or side organs of fishes and amphibians 
certain nucleated cells bearing hairs and connected with nerve 
fibres, His conclusion regarding the function of these structures 
is as follows: That the side organs “ represent a sensory appa- 
ratus especially adapted to presence in water, and for the purpose 
of appreciating mass movements of the surrounding medium 
against the body of the fish or of this against it, and also to per- 
ceive coarse waves which are promulgated by the water and which 
have longer periods of vibration than those appreciated by the 
organ of hearing.” 
Transitional forms between such of the side organs as have 
large, hyaline cylinders and which stand out directly from the 
body of the fish, and the completely covered mucous canal, are 
present. Some are described in which.the cylinder is small, rudi- 
mentary or absolutely wanting. Others still which are situated in 
a groove or depression of the surrounding skin, and some in 
which the edges of the groove overlap and thus form the transi- 
tion to the covered mucous canal. The significance of this is 
_ unmistakable. In 1868, Franz Boll (A. f. M. A. iv) investigated — 
the mucous ampullz of the snout of the shark and the Torpedo 
marmorata, and described and pictured as the essential and per- 
cipient structures of these organs cells with central and per- 
ipheral processes, and argued for the nervous continuity of the 
same. Langerhans, 1873 (A. f. M. A. ix), described the side 
organs (or organs of a sixth sense as Leydig calls them) of the 
larva of Salamandra maculosa. His results agree in every par- 
ticular with those of F. E. Schulze. Malbranc, 1876 (Z. f. W. Z. 
xxvi), also supports the results of F. E. Schulze and Langerhans 
completely. Previously the side organs had been described only 
in Jarval amphibians, but Malbranc also found them in the adult 
forms of Proteus, Siredon, Triton cristatus and teniatis. 
That the essential or percipient structure of the. side organs 
can be expressed in the same terms as the auditory, olfactory and 
taste-cells, seems indisputable, nor can we. fail to appreciate the 
_ significance of this fact. Indeed, already in 1862 Max Schultze 
expressed views regarding the identity of the nerve terminations 
in the organs of hearing, smell and taste; and in speaking of the 
common sensation of fishes, he says (Sitzbericht d. Niedl’d. Ges. 
zu Bonn. 1862), “ Here there are places in the skin where the 
nerve-cells not P E themselves into the epidermis, | but — 
