[Illustration]

SEA-SLUGS AND CUTTLE-FISH

(FROM A JOURNAL OF RESEARCHES.)

BY CHARLES DARWIN.

[Illustration:  CUTTLE-FISH.]

I was much interested, on several occasions, by watching the habits of an Octopus, or cuttle-fish.  Although common in the pools of water left by the retiring tide, these animals were not easily caught.  By means of their long arms and suckers, they could drag their bodies into very narrow crevices; and when thus fixed, it required great force to remove them.  At other times they darted, tail first, with the rapidity of an arrow, from one side of the pool to the other, at the same instant discoloring the water with a dark chestnut-brown ink.  These animals also escape detection by a very extraordinary, chameleon-like power of changing their color.  They appear to vary their tints according to the nature of the ground over which they pass:  when in deep water, their general shade was brownish-purple, but when placed on the land, or in shallow water, this dark tint changed into one of a yellowish green.  The color, examined more carefully, was a French gray, with numerous minute spots of bright yellow:  the former of these varied in intensity; the latter entirely disappeared and appeared again by turns.  These changes were effected in such a manner, that clouds, varying in tint between a hyacinth red and a chestnut brown, were continually passing over the body.  Any part, being subjected to a slight shock of galvanism, became almost black:  a similar effect, but in a less degree, was produced by scratching the skin with a needle.  These clouds, or blushes as they may be called, are said to be produced by the alternate contraction and expansion of minute vescicles containing variously colored fluids.

This cuttle-fish displayed its chameleon-like power both during the act of swimming and whilst remaining stationary at the bottom.  I was much amused by the various arts to escape detection used by one individual, which seemed fully aware that I was watching it.  Remaining for a time motionless, it would then stealthily advance an inch or two, like a cat after a mouse; sometimes changing its color:  it thus proceeded, till having gained a deeper part, it darted away, leaving a dusky train of ink to hide the hole into which it had crawled.

While looking for marine animals, with my head about two feet above the rocky shore, I was more than once saluted by a jet of water, accompanied by a slight grating noise.  At first I could not think what it was, but afterwards I found out that it was this cuttle-fish, which, though concealed in a hole, thus often led me to its discovery.  That it possesses the power of ejecting water there is no doubt, and it appeared to me that it could certainly take good aim by directing the tube or siphon on the upper side of its body.  From the difficulty which these animals have in carrying their heads, they cannot crawl with ease when placed on the ground.  I observed that one which I kept in the cabin was slightly phosphorescent in the dark.