NO. 1788. NORTH AAIERICAN EROASILID^— WILSON. 267 



After the female is once fastened to her host all further incentive 

 to free swimming disappears. She finds on the fish's gills excellent 

 aeration for her eggs and a good position from which to discharge the 

 nauplii when sufficiently matured. There is also an abundance of 

 food so that she remains there in all probability throughout life. 



The only instance of a mature female found swimming freely is 

 that of Ergasilus chautauquaensis. Both sexes of this species have 

 been taken in the tow of Lake Chautauqua in New York, and of Lake 

 Mendota in Wisconsin. The females were as abundant as the males, 

 were fully matured, and carried egg cases. As yet neither sex of 

 this species has been found on any host, so that we can not positively 

 affirm that it ever becomes parasitic, but the probability is that it 

 does. 



Prehension. — These tiny creatures fasten themselves to the gill 

 filaments, or rarely to the walls of the gill cavity, to the skin or the 

 fins, by means of the second antennae and the maxillipeds. For this 

 purpose we find both these appendages enlarged and furnished with 

 powerfid muscles. 



Their terminal joints are in the form of stout and sharp claws, while 

 they are further armed with spines and roughened surfaces to prevent 

 slipping. 



The second antennae are usually the chief organs of prehension and 

 are enlarged in nearly all the species. In the Ergasilinae they are 

 often as long as the carapace or even the entire body, while the maxil- 

 lipeds are wanting in the female. 



These antennae are thus long enough to reach around the gill fila- 

 ment and give the parasite a firm hold. 



In the Bomolochinse, however, while the second antennae are en- 

 larged and well armed with claws, spines, and roughened surfaces, they 

 are not the chief organs of prehension. But this distinction belongs to 

 the maxillipeds whose terminal joint is developed into a stout curved 

 claw, capable of grasping a gill filament or of being driven into the 

 tissue of the wall of the gill cavity, or into a fin. 



The Ergasilidae have no lunules or sucking disks, such as were found 

 among the Caligidae, and in the majority of the genera this mode of 

 prehension can not be employed. 



But in the genus Bomolochus, especially those species which fre- 

 quent the nostrils of the cod and allied fish, and in the Tseniacanthinae 

 the carapace is so arched as to act like a large sucking disk, its margin 

 being pressed close to the surface of the skin and the contact sealed 

 with mucus and water. 



This makes an effective prehensile organ in the quiet of such cavi- 

 ties as the nostrils and often obviates the necessity of setting the claws 

 into the skin. 



That the hold maintained by these parasites upon their host is 

 quite secure is realized when one tries to remove them. Long practice 



