NO. 2063. NORTH AMERICAN PARASITIC COPEPODS— WILSON. 569 



filament. The proximal end of this filament is afterwards transferred 

 to the second maxillae, which thus become the organs of prehension 

 in the adult. The hold thus secured is retained by the female through- 

 out life, the second maxillae gradually elongating and fusing with the 

 filament. In most of the species these organs become so long that 

 they entirely usurp the function of prehension, and leave the maxilli- 

 peds out of commission, so far as holding the parasite on its host is 

 concerned. 



In the male such fusion does not take place, but as soon as he has 

 found a female the second maxUlae release the frontal filament and are 

 afterwards used in anormal manner as prehensile organs along with the 

 maxillipeds. Accordingly in the male the second maxillae retain 

 their original musculature, which is similar to that of the maxillipeds. 

 And the male uses these two pairs of appendages in exactly the same 

 manner, moving about the little that it is able by employing them 

 alternately, grasping with the maxillipeds while it reaches forward 

 with the maxiUae and obtains a new hold, then releasing and reaching 

 forward with the maxillipeds. In this way the organs serve the 

 double purpose of prehension and locomotion, in fact all the locomo- 

 tion of which the adult males are capable. 



In the female, on the contrary, the musculature of the second 

 maxillae becomes highly modified. There is no further use for the 

 claws, and so the muscles that would otherwise move them become 

 atrophied. The rest of the muscles are gathered into long bands or 

 bundles, which run the entire length of the maxilla and are strong 

 enough to move the whole body. Such modified organs of prehension 

 are, so far as known, peculiar to the females of the present family, and 

 nothing like them is found in any of the other copepods. After being 

 once attached the females are incapable of any further locomotion, 

 even the sort practiced by the males so that neither pair of appendages 

 can function for this purpose. If there were not some further use for 

 the maxiUipeds we should expect to find them dwarfed or degener- 

 ated, but they retain to the fuU their shape and powerful musculature. 

 This is because the female uses them in procuring her food. Ordi- 

 narily her body hangs free from the host, supported solely by the 

 second maxillae. In order to obtain requisite nourishment the head 

 and mouth of the parasite must be drawn up to, and held in contact 

 with, the skin of the host. This is done by means of the maxUhpeds, 

 and is fully as important a function as the one served by the second 

 maxillae. 



Hosts. — This family of parasites is widely distributed amongst 

 fishes in both salt and fresh water. Some of our best food and game 

 fish are infested with them, and when they once obtain entrance to 

 a stock pond, fish hatchery, or aquarium they usually multiply so 

 rapidly as to become a serious nuisance, and may even kill the fish. 



