28 THE STORY OF LIFE IN THE SEAS. 



general features that we find in the other Verte- 

 brates. Lobsters, Crabs and Prawns have each 

 a pair of stalked eyes, which are probably as 

 perfect in their functions as the Vertebrate 

 eye, although built up on an entirely different 

 model. Whelks, Winkles, and other Gastropods, 

 although so slow in their movements, have each, 

 upon or close to their tentacles, a pair of minute 

 eyes, which are much simpler and probably far 

 less perfect in form than the eyes of their more 

 highly organised neighbours. Even the little 

 Jelly-fish, Star-fish, Sea-urchins, and other creep- 

 ing forms of life, are provided with specialised 

 pigment spots, which we have good reason to 

 believe enable them to perceive the rays of 

 light. 



But we must notice that it is only the animals 

 that are capable of locomotion from place to 

 place that need these organs of vision, and that 

 the stationary forms are blind. In the large 

 class of the Lamellibranchs, for example, to which 

 the Oyster and the Mussel belong, we find that 

 with a few exceptions there are no eyes. These 

 animals, after the first few stages of their" life 

 are past, settle down into the sand, or fasten on 

 to a rock and remain there until their life is 

 clone. Their food, consisting of the minutest 

 specks of animal and vegetable life, is brought 

 to them by the sea-currents ; they do not need 

 nor desire to seek the society of their relations, 

 and when their enemies approach they resign 

 themselves almost without an effort to the inevi- 

 table. To such animals eyes would be useless, 

 and so nature has withheld them. 



