486 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvm. 



the sides of the dish or aquarium as far as possible above the surface 

 of the water and remaining there till thoroughly dried, and, of course, 

 dead and worthless. For this reason it is very difficult to keep such 

 species alive for any length of time. Even to cany them from the 

 collecting ground to the laboratory, or to keep them alive while being 

 examined, it is necessary to carefully stopper the bottle or to cover 

 the dish, so that the air above the water shall be so saturated with 

 moisture that the copepods can not dry in it. 



Fortunately this disagreeable habit is practically confined to the genus 

 Ci digits, and the other genera make quite tractable subjects for aquaria. 

 This is particularly the case with Lepeophtheirus, and A. Scott states 

 that L. pectoralis may be kept- alive "in sea water for upward of six 

 weeks after removal from the fish." 



PREHENSION. 



The organs of prehension include both sucking disks and claws; the 

 former are confined to a few genera; the latter are common to all the 

 genera. The arched carapace, also, in all the genera, acts as a large 

 sucking disk, its margin being pressed close to the surface, and the 

 contact sealed with water and slime. This constitutes a secondary 

 organ of prehension, vastly more effective than in the Argulidae, 

 since its margin is made continuous posteriorly by the broad lamina 

 connecting the third swimming legs. When flattened against a sur- 

 face by muscular contraction and then released it works very 

 powerfully. 



The claws constitute the terminal joints of the second antennee and 

 the second maxillipeds, the entire joint functioning and being capable 

 of strong flexure upon the basal joint. . 



It seems probable that these different organs of prehension are used 

 in different localities upon the fish's bod}^. The lunules and the suc- 

 tion of the carapace afford the principal means of prehension on those 

 portions of the outside surface of the host which are covered with 

 scales. There is an integument over the scales, to be sure, and in 

 many of the fish which serve as hosts the scales have small spines upon 

 their free surfaces. But the integument is so thin and the spines are 

 so small and weak that they afford but a feeble hold for claws. There 

 is no chance to bury the claws sufficiently to withstand the ordinary 

 friction of water, to say nothing of that of sand or mud, which must 

 be overcome on the ventral surface of such fish as the flounder, skate, 

 etc. The fins, on the other hand, have no scales and the covering 

 integument is firmer and thicker, and affords an admirable material in 

 which the claws may fully bury themselves. So that although the tail 

 and other fins must, from their movements, subject the parasites to 

 considerable additional friction, this is more than counterbalanced by 

 the superior hold which they afford. The blood vessels also are more 



