486 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



the sides of the dish or aquarium as far as possible a1)ove the surface 

 of the water and reniaiuino- there till thoroughly dried, and, of course, 

 dead and wortldess. For this reason it is very ditHcult to kee[) sueh 

 species ali\ c for any length of time. K\en to carry them fiom tlie 

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

 examined, it is necessary to carefully stopper the bottle oi" to cover 

 the dish, so that the air al)ove the water shall be so saturated with 

 moisture that the copepods can not dry in it. 



Fortunately this disagreeable habit is practically contined to the genus 

 ( 'til!(/iis, and the other genera make ([uite tractable sul)iects for aquaria. 

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

 that L. pectond'tK may be kept alive ''in sea water for upward of six 

 weeks after removal from the tish." 



PREHENSION. 



The oi-gans 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 etfective than in the Argulida?, 

 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 ver}" 

 powerfully. 



The claws constitute the terminal joints of the second antennw and 

 the second maxillipeds, the entire joint functioning and being capable 

 of strong flexure upon the basal joint.. 



It seems proI)able that these ditt'erent organs of prehension are used 

 in diflerent localities upon the flsh's body. The lunules and the suc- 

 tion of the carapace aflord 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 flsh 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 aflord but a feeble hold for claws. There 

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

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

 l)e overcome on the ventral surface of such flsh as the flounder, skate, 

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

 integument is flrmer and thicker, and afl'ordsan admirable material in 

 which the claws may fidl\' bury themselves. So that altlu)ugh the tail 

 and other tins must, from their mo\(Mnents, sul)ject the parasites to 

 considerable additional friction, this is more than counterl)alanced b}" 

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



