ANIMAL LOCOMOTION 203 



itself up into the air for a distance of a yard or 

 more. The lobster also indulges in a peculiar form 

 of locomotion. When alarmed it spreads out its 

 tail and curls it up beneath its body with such 

 rapidity as to force itself backwards through the 

 water. 



The majority of crabs are only able to move along 

 the ground with that curious sideways gait that is 

 so familiar to every one, but the members of the 

 genus Portunus, of which the velvet crab is a well- 

 known species found around our coasts, are capable 

 of swimming through the water by means of their 

 hind legs, which terminate in flattened and oar-like 

 growths. Then, again, the five-fingered star-fish 

 is provided with numerous tentacles or tube-feet 

 upon the under surface of its rays, by the use of 

 which it can crawl slowly along the ground, covering 

 a distance of two inches during the course of a 

 minute. The jelly-fish, although very helpless and 

 unable to control the direction of their course 

 through the water, are, nevertheless, able to make 

 some progress by alternately expanding and con- 

 tracting their bell-like bodies. 



