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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 94 



is much freedom of motion in every one of the articulations, and the 

 body can be flexed considerably upward or downward, to the right 

 or to the left, as may be necessary. This increased flexibility enables 

 the copepod to realize fully all the advantages of its modified size 

 and shape. If one of these copepods is put in an aquarium with sand 



Fig. 2. — a, dorsal view of a female Paralcptastaciis brezncauda- 

 tus, a sand dweller ; h, dorsal view of a male Eniertonia gracilis, 

 a sand dweller. 



at the bottom, it quickly buries itself in the sand, and during the process 

 gives abundant evidence of its great flexibility. 



Another useful modification is an increase in tactile equipment and 

 sensibility. These terraqueous copepods are compelled to move about 

 more or less in the dark, where their eyesight can be of little use for 

 guidance. At the same time the space within which they move is so 



