36 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Although the Amphipoda possess three dififerent kinds of 

 locomotor organs, the pereiopods, pleopods, and uropods, which 

 are used respectively for crawling, swimming, and leaping, it is 

 only in a few species of Orchestiidse that we find all three methods 

 of locomotion employed. Unlike many of the higher crustaceans 

 locomotion is always forward. The most general method is 

 swimming. In order to obtain a start in swimming the animal 

 usually extends the abdomen with some vigor — this part of the 

 body being carried, when the animal is at rest, curled up beneath 

 the body — and then maintains its motion by means of the rapid 

 vibration of the pleopods. In swimming vertically, however, 

 the abdomen frequently aids in the propulsion of the body, as 

 in starting. While swimming, the body is well straightened, the 

 antennas are held out in front of the body and move slightly as 

 if exploring, and the pereiopods are held directed backwards. 

 The animal seems to have some difficulty in maintaining its 

 balance for it frequently rolls over and swims with its back or 

 one side or the other downwards. 



In walking or crawling there are two quite distinct methods. 

 In those species whose bodies are depressed like Corophium, for 

 example, the body is easily maintained in an upright position and 

 supported by the pereiopods. Where the body is strongly com- 

 pressed, however, the upright position is with difficulty held and 

 the last two pairs of pereiopods are bent outwards to brace the 

 body. In these forms it is far more usual for the animal to lie 

 on its side and progress by the alternate flexion and extension 

 of the body with the corresponding movements of the pereiopods. 



Jumping is resorted to only by Orchcstia and Talorchcstia, 

 and in these forms only when the animal is startled and must 

 escape quickly. This act is accomplished by the uropods and the 

 abdomen which is extended suddenly. Orchestia agilis can easily 

 spring more than a foot into the air. The jumping is usually 

 aimless and as a result the animal frequently falls upon an 

 tinfavo table spot. 



In climbing over algas and other irregularities of the bottom, 

 many species employ their antennae as hooks for pulling the body, 

 but the gnathopods are more generally used for this purpose. 



Burrowing has been studied most carefully by Miss Small- 

 wood in Talorchestia which lends itself to the observation of this 



