200 COLE. [VOL. II. 



We are now in a position to examine more carefully the 

 variations in the actions of the different individuals when 

 placed in the water. As mentioned before, if the animal treads 

 vigorously enough to overcome the force of gravity, it will swim ; 

 and so long as the body remains exactly in a horizontal posi- 

 tion it will only move directly up or clown according to the 

 vigor of the strokes ; but as soon as the body gets out of this 

 plane the animal will progress through the water in the direc- 

 tion in which its dorsal surface is turned. For it to remain in 

 a horizontal plane it is necessary that the legs should all beat 

 with equal force ; but as a matter of fact the anterior legs beat 

 of teucr and with more vigor than the posterior legs, thus raising 

 the anterior end and tilting the animal backward. I did not 

 make out any regular order of movement of the legs further 

 than this, that the posterior legs seem to lack the vigor and 

 strength and to be less under the control of the animal than 



o 



the anterior pairs. A specimen which does not tread fast 

 enough to raise itself from the bottom, or possibly one whose 

 specific gravity is greater, crawls or walks straight ahead upon 

 the sand, apparently, at first sight, much as an insect walks ; 

 but upon closer examination it may be seen that most of the 

 movement is accomplished by the first pair of legs, assisted to 

 some extent by the second, while the third and fourth pairs 

 seem to be a hindrance rather than a help. By reference to 

 Fig. 2 it can be seen how the anterior legs, by hooking into 

 the sand, can pull the animal forward ; while for the fourth pair 

 to help in the forward movement it would be necessary for 

 them to push, which would require a motion exactly the reverse 

 of that which has been described for them when free from the 

 bottom. Instead of this they drag along in a sort of helpless 

 fashion, seeming to attempt the same movement as before, but 

 hindered by striking the sand and by the forward movement of 

 the animal as a whole due to the stronger anterior legs. A 

 considerable backward and forward movement is now to be 

 observed in the second and third legs, but this is probably also 

 due to the pulling forward of the body after the legs are put 

 down onto the sand, and not to a direct action of the legs 

 themselves, the motion being allowed for, as before stated, by 



