Page:Popular Science Monthly Volume 21.djvu/773

Rh arms of the cuttle-fish head as the representatives of the missing velum. But, as the latter organ always exists on the dorsal or upper side of the mouth, and as the arms are placed originally behind and under the cuttle-fish mouth, the correspondence of arms and velum has not been accepted by zoölogists. On the other side stands out the opinion of Huxley, who regards the "arms" of the cuttle-fish head as more truly corresponding with the "foot" of the mussel, snail, and other mollusks.

The margins of the foot, in this view of matters, have been prolonged in the young cuttle-fish to form eight, ten, or more arms, and the front and sides of the foot, having overgrown the mouth, are united in front, so that the mouth appears to be placed in the center of the foot, instead of in front and above it, as in other mollusks. So, also, most naturalists maintain, and with every appearance of correctness, that the characteristic "funnel" of the cuttle-fishes—to be hereafter referred to—is an organ formed by two side-processes of the foot, named epipodia. Adopting the view thus sanctioned by competent authority, we may trace in a cuttle-fish the highly modified form of a snail or whelk, and the still more modified form of the mussel tribes. The foot, instead of growing backward and downward as in the snail, and thus forming a broad walking disk, comes to grow over the mouth in front. So that, placing a cuttle-fish in structural comparison with a whelk or mussel, we should have to set it head downward, when the foot (or arms) would be lowest, and the great bulk of the body, with the heart uppermost, would be situated, as in the snail, above the foot.

The group of the cuttle-fishes may be said to divide itself in the most natural fashion into two main divisions. The first of these groups includes all living cuttle-fishes save one—the pearly nautilus. This first division is that of the Dibranchiates, or two-gilled cuttlefishes. The familiar octopus (Fig. 1), the loligos or squids, the sepias, and the argonauts or paper nautili, are among the best known of its representatives. The second group is represented by a single living cuttle-fish, the pearly nautilus (Nautilus Pompilius), just mentioned, and by many fossil and extinct forms.

One of the most remarkable traits of cuttle-fish existence is the curious play of "shot" colors which takes place in their integument. I have seen a loligo, or squid, stranded on the sea-beach make glorious its dying agonies by a play of colors of the most astounding description. The natural purplish tint of the body was now and again deepened to well-nigh a dark blue; the slightest touch served to develop a patch of angry pink; and continually over the whole surface of the body the hues and tints, ranging from dark purple to light red, succeeded each other in rapid array.

The assimilation of an animal's color to the surfaces on which it rests forms a notable circumstance of zoology, which has been