The Sense of Touch.—The sense of touch is better developed among fishes. Most of them flee from contact with actively moving objects. Many fishes use sensitive structures as a means of exploring the bottom or of feeling their way to their food. The barbel or fleshy filament wherever developed is an organ of touch. In some fishes, barbels are outgrowths from the nostrils. In the catfish the principal barbel grows from the rudimentary maxillary bone. In the horned dace and gudgeon the little barbel is attached to the maxillary. In other fishes barbels grow from the skin of the chin or snout. In the goatfish and surmullet the two chin barbels are highly specialized. In Polymixia the chin barbels are modified branchiostegals. In the codfish the single beard is little developed. In the gurnards and related forms the lower rays of the pectoral are separate and barbel-like. Detached rays of this sort are found in the thread-fins (Polynemidæ), the gurnards (Triglidæ), and in various other fishes. Barbels or fleshy flaps are often developed over the eyes and sometimes on the scales or the fins.
Fig. 90.—Goatfish, Pseudupeneus maculatus (Bloch). Woods Hole.
The structure of the lateral line and its probable relation as a sense-organ is discussed on page [23]. It is probable that it is associated with sense of touch, and hearing as well, the internal ear being originally "a modified part of the lateral-line system," as shown by Parker,[8] who calls the skin the lateral line and the ear "three generations of sense-organs."
The sense of pain is very feeble among fishes. A trout has been known to bite at its own eye placed on a hook, and similar insensibility has been noted in the pike and other fishes. "The Greenland shark, when feeding on the carcass of a whale, allows itself to be repeatedly stabbed in the head without abandoning its prey." (Günther.)
FOOTNOTES:
[8] See Parker, on the sense of hearing in fishes, American Naturalist for March, 1903.