Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

6 ST. JAGO — CAPE DE VERD ISLANDS. Jan. 1832. series : the height of the cliff thus affording a rude measure of the age. Durino- our stay, I observed the habits of some marine animals. A large Aplysia is very common. This sea-slug is about five inches long ; and is of a dirty yellowish colour, veined with purple. At the anterior extremity, it has two pair of feelers ; the upper ones of which resemble in shape the ears of a quadruped. On each side of the lower surface, or foot, there is a broad membrane, which appears sometimes to act as a ventilator, in causing a current of water to flow over the dorsal branchiae. It feeds on delicate sea-weeds, which grow among the stones in muddy and shallow water and I found in its stomach several small pebbles, as in the gizzards of birds. This slug, when disturbed, emits a very fine purplish-red fluid, which stains the water for the space of a foot around. Besides this means of defence, an acrid secretion, which is spread over its body, causes a sharp, stinging sensation, similar to that produced by the Physaha, or Portuguese man-of-war. 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 cre- vices ; and when thus fixed, it reqviired great force to remove them. At other times they darted tail first, with the rapi- dity of an arrow, from one side of the pool to the other, at the same instant discolouring the water with a dark chestnut- brown ink. These animals also escape detection by a very extraordinary, chameleon- like, power of changing their colour. They appear to vary the 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 colour, examined more carefuUy, was a French gray, with numerous minute spots of bright yellow : the former of these varied in intensity ; the latter