50 THE STORY OF LIFE IN THE SEAS. 



the body brought about by the dilatations of these 

 vesicles is extremely rapid. Many other animals 

 have the power of changing colour, but in no 

 group is the alteration more rapid and remark- 

 able than in this order of Cuttlefishes and Squids. 

 Another very interesting feature presented by 

 these animals is their ability to discharge sud- 

 denly a cloud of inky substance into the water. 

 Their principal enemies are the Whales, Por- 

 poises and some of the larger Sharks and other 

 Fish. When these animals approach, or any 

 other danger is feared, the Cuttlefishes discharge 

 into the water from a special bag, called the ink- 

 sac, a quantity of black or brown pigment 

 which, diffusing rapidly, forms a cloud round 

 their bodies, in the obscurity of which they 

 frequently escape pursuit. The well - known 

 Sepia of painters is obtained from these ink- 

 sacs. 



The last group of animals occurring among the 

 rocks are those capable of vigorous swimming 

 movements. Many Crustaceans, such as the 

 Lobsters and Prawns, are capable, as has just 

 been pointed out. of swimming rapidly through 

 the water by means of their powerful tails. But 

 this swimming power is only accessory to that of 

 crawling or creeping, and is used merely when 

 the animals are disturbed. Cuttlefishes and their i 

 allies seem to spend a considerable portion of 

 their time in floating or swimming in the water, 

 but still they do crawl about among the rocks, 

 and very probably attack and feed upon their 

 prey entirely upon the sea-bottom. 



The members of the Rock-fauna which belon; 



