j-2 HOLMES. [\'OL. II. 



Amphithoe steers itself while swimming by altering the exten- 

 sion of the abdomen and by rolling from side to side. Lateral 

 bendings of the body could not be seen to play a part in 

 directing the swimming motions, although I have observed 

 this method of steering employed by other amphipods. 



Amphithoe longimana, like many other amphipods, is unable 

 to walk over a plane surface. When out of water it is able to 

 make indifferent progress by the characteristically amphipodan 

 gliding movements produced by alternately flexing and extend- 

 ing the abdomen. It is utterly incapable of leaping like the 

 sand fleas and some of their aquatic relatives. Owing to its 

 compressed form, it is unable to maintain itself upright while out 

 of water, or even in water, unless it has some object to which it 

 can lay hold. In its characteristic habitat among the seaweed, 

 Amphithoe crawls with considerable agility. The principal 

 organs for crawling are the second antennae, the two pairs of 

 gnathopods, the third and fourth pairs of pereopods, and to a cer- 

 tain extent the abdomen. The antennae are thrown over objects 

 and flexed, thus tending to pull the body upward and forward. 

 The gnathopods are used to seize objects in order to pull 

 the body along. The two following pairs of appendages are 

 employed much as the walking legs of insects, although they 

 move in a nearly vertical plane. The abdomen assists in loco- 

 motion by being thrust forward beneath the body until the tip 

 is hooked on to some irregularity of the surface over which the 

 animal is moving when it is extended, thus giving the body a 

 forward impulse. The movement recalls the leaping motion 

 effected by the abdomen in the sand fleas. In fact, very 

 similar motions are performed in both cases, but in Amphithoe 

 the motions are much less rapid and energetic. The ambula- 

 tory movements of this species are never rapid, owing doubtless 

 to the necessity for keeping the body from falling over on its 

 side. The last three pairs of thoracic legs, although not used 

 directly for locomotion, are indirectly of service in holding the 

 body upright. These appendages, which are bent over the back 

 and have their claws pointing forward, are used to hook on to 

 objects and thus act as organs of support while progression is 

 effected by the other appendages of the body. 



