Fig. 88.—Brook Lamprey, Lampetra wilderi Jordan and Evermann. (After Gage.) Cayuga Lake.
The otoliths, commonly two in each labyrinth, are usually large, firm, calcareous bodies, with enamelled surface and peculiar grooves and markings. Each species has its own form of otolith, but they vary much in different groups of fishes.
Fig. 89.—European Lancelet, Branchiostoma lanceolatum (Pallas). (After Parker and Haswell.)
In the Elasmobranchs (sharks and rays) and in the Dipnoans the ear-sac is enclosed in the cartilaginous substance of the skull. There is a small canal extending to the surface of the skull, ending sometimes in a minute foramen. The otoliths in these fishes are soft and chalk-like.
The lancelet shows no trace of an ear. In the cyclostomes, hagfishes, and lampreys it forms a capsule of relatively simple structure conspicuous in the prepared skeleton.
The sense of hearing in fishes cannot be very acute, and is at the most confined to the perception of disturbances in the water. Most movements of the fish are governed by sight rather than by sound. It is in fact extremely doubtful whether fishes really hear at all, in a way comparable to the auditory sense in higher vertebrates. Recent experiments of Professor G. H. Parker on the killifish tend to show a moderate degree of auditory sense which grades into the sense of touch, the tubes of the lateral line assisting in both hearing and touch. While the killifish responds to a bass-viol string, there may be some fishes wholly deaf.
Voices of Fishes.—Some fishes make distinct noises variously described as quivering, grunting, grating, or singing. The name grunt is applied to species of Hæmulon and related genera, and fairly describes the sound these fishes make. The Spanish name ronco or roncador (grunter or snorer) is applied to several fishes, both sciænoid and hæmuloid. The noise made by these fishes may be produced by forcing air from part to part of the complex air-bladder, or it may be due to grating one on another of the large pharyngeals. The grating sounds arise, no doubt, from the pharyngeals, while the quivering or singing sounds arise in the air-bladder. The midshipman, Porichthys notatus, is often called singing fish, from a peculiar sound it emits. These sounds have not yet been carefully investigated.
The Sense of Taste.—It is not certain that fishes possess a sense of taste, and it is attributed to them only through their homology with the higher animals. The tongue is without delicate membranes or power of motion. In some fishes certain parts of the palate or pharyngeal region are well supplied with nerves, but no direct evidence exists that these have a function of discrimination among foods. Fishes swallow their food very rapidly, often whole, and mastication, when it takes place, is a crushing or cutting process, not one likely to be affected by the taste of the food.