646 PROCEEDINGS OF THE NATIONAL MUSEUM. 



But we may reasonably infer that, after withdrawal from its host 

 for the purpose of egg laying, if an Argulus is una])le to tincl another 

 fish of the same speeies it is willing to take almost any temporar}' host 

 obtainable, transferring afterwards as opportunity offers. In confir- 

 mation of such an inference the following experiments were made on 

 A. cdtostomi and A. versicolof for fresh-water forms and on ^1. lati- 

 couda and A. raegalop^ from salt-water fishes. 



1. ^4. catostomi is usually found upon the common ''sucker/' Catos- 

 tomus commersonii (Lacepede), from which it was originally obtained 

 and named, but it also occurs, and in the authors experience even 

 more abundantly, upon the chub sucker, Eriinyzoi) sueefta ohhnuiua 

 (Mitchill). 



It was desired to keep some of these parasites through the breeding 

 season and also to ascertain, if possible, how they find and attach 

 themselves to their host. But suckers are large and clumsy fish, 

 difficult to transport, and requiring large aquaria. Added to this is 

 the fact that the easiest method of obtaining them at the season when 

 the Arguli are breeding is b}' spearing, and that this usually kills the 

 fish. 



For these reasons they were removed from the suckers and trans- 

 ported to the laboratory in jars. It was evident, however, that they 

 could not be kept for any length of time without a host, and accord- 

 ingly several species of fish were tried, the sunfish {Lepomis gibhosm 

 Linnseus), the dace {Notropis megalopi< Rafinesque), the yellow perch 

 {P. flavescens Mitchill), and a species of minnow, locally known as the 

 "mummichug." When the fish were placed in the aquarium, the 

 Arguli very unexpecj:edl3^ paid no attention to them and did not appear 

 to recognize their presence in any way, and yet several days had 

 elapsed before the fish could be obtained, and the parasites must have 

 become quite hungry. 



But they continued swimming about in their usual lazy, erratic 

 fashion, often passing very close to one of the fish, but never seeming 

 to realize that it might become a possible host, until they actually ran 

 plump into it. Then, however, they made up for lost time, fastened 

 themselves to the fish's body instantly, and eagerly sought for a place 

 to pierce the skin and obtain some blood. On these small fish the 

 bases and surfaces of the fins (including the tail), and the thin skin 

 under the throat were favorite localities. They stopped at one of 

 these places long enough to obtain a good meal and thi^n passed for- 

 ward and tried to crawl beneath the operculum. 



If they failed in this on account of the small size of some of the fish 

 they seemed content to remain upon the external surface, and in this 

 way specimens were carried successfully through the l)reeding season 

 and a fine lot of eggs obtained. 



There was no hesitation in attaching to any of these fish, and there 

 seemed to be no choice between the species. 



