328 PROCEEDINOS OF THE NATIONAL MUSEUM. vol. xxxiii. 



LOCOMOTION. 



The female has entirely lost the power of free swnnining, and 

 almost entirely that of moving about on her host. She can and does 

 change her position, but only for the most strenuous reasons and 

 during the earlier stages of development. Such motion is of neces- 

 sity very slow, since it involves the loosening and refastening of the 

 hold maintained by the different prehensile organs. Some of them 

 must remain fastened all the time, and the only progress made is the 

 distance that can be covered by the stretching of the body between 

 the alternate fastenings. When removed from the fish and placed 

 in an aquarium these females simply lie upon their backs, moving 

 the swimming legs spasmodically, but producing no change of position 

 at all. The males, on the contrary, can swim as freely as aligns, 

 and when placed in an aquarium with the latter they resemble them 

 so closely in form and movements as to be distinguished only by 

 carefid scrutiny. Accordingly we should expect to find some of the 

 males swimming about freely at the breeding season, like those of 

 Caligus, and there are in the U. S National Museum collection 

 several specimens so recorded. 



None of either sex, so far as known, have lunules on the frontal 

 plates, and hence they do not exhibit the scuttling movements 

 characteristic of Argulus and Caligus. And yet they can move about 

 easily and rapidly over the outside of the shark's body and are by 

 no means confined to tne immediate vicinity of the females. This 

 motion is accomplished b}^ means of the adhesion pads, maxillipeds, 

 and swimming legs. The former hold the copepod to the skin of its 

 host, while the latter push the body forward. Instead of a scutthng 

 movement, therefore, each side of the body being advanced alter- 

 nately, there is a forward gliding motion of the entire body, similar 

 to that shown in swimming. All four pairs of swimming legs in 

 these males are biramose, and the rami are wide flattened laminae 

 which propel the animal swiftly through the water. 



There is no broad basal apron coimecting the third legs across the 

 mid line, which was characteristic of the Caliginge, but this is largely 

 compensated by the fact that the fourth legs are as broad and pow- 

 erful as the third pair, while in the Caliginse they were of no actual 

 service for swimming. 



PREHENSION. 



The organs of prehension include adhesion pads, claws, and mod- 

 ified chelae. The adhesion pads are common to all the genera and 

 to both sexes; they arise as accessory organs in connection with the 

 various appendages, and are usually of different shapes in the different 

 genera and even in the different species, thereby affording good 



