20 A SEA SLUG. [chap. 



of the stream, It is converted into groups of beautiful 

 radiated fibres resembling arragonite. The beds of hi\ 

 rise in successive gently-sloping plains, towards the Interic 

 whence the deluges of melted stone have originally pr 

 ceeded. Within historical times, no signs of volcar 

 activity have, I believe, been manifested in any part 61 

 St. Jago. Even the form of a crater can but rarely be 

 discovered on the summits of the many red cindery hills 

 yet the more recent streams can be distinguished on the 

 coast, forming lines of cliffs of less height, but stretching 

 out in advance of those belonging to an older series : the 

 height of the cliffs thus affording a rude measure of the a 

 of the streams. 



II 



During our stay, I observed the habits of some marl 

 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. 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 or lungs. It feeds on the 

 delicate sea-weeds which grow among the stones in muddj 

 and shallow water ; and I found in Its stomach several 

 small pebbles, as in the gizzard of a bird. This slug, when 

 disturbed, emits a very fine purpllsh-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 Physalia, 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 

 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 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 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 



