If nudibranchs and other marine invertebrates be protectively coloured, there must be corresponding perceptual powers in the fishes that are thus led to avoid them; for there seems to be definite avoidance, and not merely indifference. This, however, might be made the subject of further experiment, not only with fishes, but with other animals. I tried some chickens with currant-moth caterpillars, to each of which I tied with thread a large looper. Some of them would have nothing to do with the unwonted combination. But one persistently pecked at the looper, and tried to detach it from its fellow-prisoner. Though, on the whole, there was some tendency for aversion to the currant-moth caterpillar to overmaster the appetence for the looper, I was not altogether satisfied with the result of the experiment. But I think that if the protectively coloured larva had been regarded with mere indifference (i.e. neither aversion nor appetence), the appetence for the loopers should have made the chickens seize them at once. To return to fishes. It is probably difficult or impossible for us to imagine what their constructs are like; but that they, too, proceed to define them by examination seems to be a legitimate inference from some of their actions. Mr. Bateson says, "The rockling searches [for food] by setting its filamentous pelvic fins at right angles to the body, and then swimming about, feeling with them. If the fins touch a piece of fish or other soft body, the rockling turns its head round and snaps it up with great quickness. It will even turn round and examine uneatable substances, as glass, etc., which come in contact with its fins, and which presumably seem to it to require explanation."[GO] And, speaking of the sole, the same observer says,[GP] "In searching for food the sole creeps about on the bottom by means of the fringe of fin-rays with which its body is edged, and, thus slowly moving, it raises its head upwards and sideways, and gently pats the ground at intervals, feeling the objects in its path with the peculiar viliform papillæ which cover the lower (left) side of its head and face. In this way it will examine the whole surface of the floor of the tank, stopping and going back to investigate pieces of stick, string, or other objects which it feels below its cheek." If we admit the fact that carp come to be fed at the sound of a bell, we have evidence that some fishes can associate an arbitrary sound with the advent of things good to eat. But it is, perhaps, better at present to regard the fact as one requiring verification.