SWIMMING ANIMALS 105 



Seal {Phoca uitalina) and the Grey Seal (Halichourus 

 grvpus). Neither of these furnish the beautiful sealskin 

 of commerce, this product only being obtained from 

 certain distinct species known as " fur seals " or " sea 

 bears." 



Seals feed mostly on fish, and are commonly a nuisance 

 in the estuaries of some of the Scottish salmon rivers, where 

 they do much damage to the net fisheries for the salmon. 

 Some species feed on shellfish and other small marine 

 animals. The walrus uses its long ivory tusks for 

 digging in the sand and gravel to turn up the shellfish 

 on which it feeds. 



Cuttlefishes and Squids 



Amongst invertebrate animals there is only one group 

 which can bd classed as true swimming animals. These are 

 the cuttlefishes and squids, which belong to the family 

 known as Cephalopods. This name is derived from two 

 Greek words meaning " head " and " foot," and originates 

 from the fact that actually the feet or tentacles surround 

 the head. 



The Cephalopods belong to that main division of the 

 backbone-less animals known as Molluscs, and are closely 

 allied therefore to oysters, mussels and cockles, though 

 admittedly the external resemblance is not obvious. In 

 many ways they are the most highly evolved of the back- 

 boneless animals and are remarkable .for possessing eyes 

 similar in almost all respects to those of the higher animals 

 such as fish and mammals. 



Both the cuttlefish and the squid possess ten tentacles 

 armed with suckers. Two of these tentacles are very much 

 longer than the others and can be withdrawn into a cavity 

 near the head. In this respect they differ from their near 



