GENERAL NOTES ON FISHES. 561 
distribution of the pigment granules in the cells is altered. In shallow 
and clear water this power of colour-change may be protective, but an 
appreciation of the protective value of colouring demands careful 
attention to the habits and habitat of the fishes, to the nature of the 
ig in which they live, and to the enemies which are likely to attack 
them. 
Food.—The food of Fishes is very diverse — from Protozoa to 
Cetaceans. Sharks and many others are voraciously carnivorous ; 
many engulf worms, crustaceans, insects, molluscs, or other fishes; 
others browse on seaweeds, or swallow mud for the sake of the living 
and dead organisms which it contains, Their appetite is often 
enormous, and cases are known (4g. Chéasmodon niger) where a fish 
has swallowed another larger than its own normal size. Many fishes 
follow their food by sight ; many by a diffuse sensitiveness, to which it 
is difficult to give a name; a few, it would seem, by a localised sense 
of smell. It is important to realise that fishes depend very largely on 
small crustaceans, and these again on unicellular plants and animals, 
Just as we may say that all flesh is grass, so we may say that all fish is 
Diatom. 
Senses, etc.—Fishes do not seem to have much sense of taste or of 
smell, but diffuse sensitiveness to touch, chemical stimuli, etc., is well 
developed, especially on the head and along the lateral line. Though 
there is no drum, and the ear is deeply buried, a few seem to hear. 
Some experiments suggest that the semicircular canals of the fish’s ear 
are indispensable in the direction or equilibration of movement. The 
sense of sight is, on the whole, well developed, and many have 
“¢ darkness eyes.” As to the intellectual powers of their small brains 
we know little, but many show quickness in perceiving friends or foes, 
a few give evidence of memory, and many of their instincts are complex. 
At the breeding season there is sometimes an elaborate expression of 
excitement, well seen in the stickleback. 
Reproduction. — Hermaphroditism is constant in some bony 
fishes, e.g. Chrysophrys auratus (dichogamous), and three species 
of Serranus (autogamous); almost constant in Pagellus mormyrus ; 
very frequent in Box salga and Charax puntazzo; and exceptional 
in over a score of fishes, such as sturgeon, cod, herring, pike, and 
carp. The simplicity of the genital organs and their ducts may 
in part explain why casual hermaphroditism is more frequent in 
Fishes than in higher Vertebrates. In many cases the males are 
smaller, brighter, and less numerous than the females. Courtship 
is illustrated by the sticklebacks (Gasterosteus, etc.), the paradise- 
fish (Macropodus), and others; and many male fishes fight with 
their rivals. ‘ 
Most fishes lay eggs which are fertilised and develop outside of the 
body. They may be extruded on gravelly ground, or sown broadcast 
in the water. Sturgeon, salmon, and some others ascend rivers for 
spawning purposes, while the eels descend to the sea, In the case of 
trout, Barfurth has observed that the absence of suitable spawning 
ground may cause the fish to retain its ova. This results in ovarian 
disease, and in an inferior brood next season. Except in Elasmo- 
branchs, the ova are relatively small, and large numbers are usually 
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