DORSAL VIBIJATILE FIN OF THE ROCKLING (MOTELLA). 253 
when the food is placed in actual contact and is due to the 
co-related reflexes of touch and taste ; (3) a reaction similar 
to the last, but not so definite, and which is observed when 
the food is not actually in contact, but only in the proximity 
of the taste-buds : this may be regarded as a purely gustatoiy 
response; (4) a tactile reaction, to which the fish at first 
responds, but after repeated experiments and then an interval 
only reacts in a tentative or incjuiring manner, with a 
deliberate movement. 
The main purpose of this paper is to indicate that the 
vibratile fin of the rockling is morphologically, as indicated 
by Bogoljubsky, a modified part of the ordinary dorsal fin, 
and physiologically a part which, together with the adjacent 
skin, forms a highly efficient food-locating or food-detecting 
organ . 
A general correspondence in structure allows us to deduce 
that this oral fin is morphologically a modification of the 
aboral fin. The anterior rays of the aboral agree with those 
of the oral fin in general structure, and the two fins are 
directly connected with one another by a ligament, although 
there is a slight external interval between them. 
As regards the physiological side, it has already been noted 
that the vibration of the rays keeps the skin on either side, on 
which the taste-buds are situated, clear of sand particles, etc. 
One has also to remember that internal taste-buds are usuallj^ 
associated, as in mouth, pharynx, gill-chambers, etc., with a 
current of water. I would also suggest that as the rockling 
is phlegmatic in its habits, and lives on the shore under 
stones in more or less still water during at least half its life- 
time, or on the bottom in deeper water, the advantage of 
vibrating processes driving currents of water is obvious; this 
vibration no doubt aids in bringing indications of food. The 
experiments of Herrick with other fish, showing that these 
detected the presence of food by means of the taste-buds 
more quickly in running than in still water, is of interest in 
this connection. 
As regards the belief held by some zoologists that the 
