AMERICAN PARASITIC ARQ ULID.T^ WILSON. 651 



that could happen, wince it tends to keep the general tone down to 

 the level of the weaker and poorer individuals. Hence the breeders 

 of tish and the keepers of aquaria often find these parasites trouble- 

 some pests, as was clearly stated by the very lirst observer, Leonard 

 Baldneur (1660). 



In the manuscript left in the public.' librar}^ at Strassburg, while 

 speaking of what he calls the ''pou des poissons" (A. Jvliaceu^), he 

 says that it is seldom found in the environs of Strassburg except upon 

 trout, and that it frequenth" kills them, especially those which are 

 kept in ponds. 



In view of these difficulties the following experience will prove of 

 interest and may become of practical value b}^ suggesting an easy and 

 efi'ective means for keeping the pests Avithin due bounds: In the town 

 of Warren, Massachusetts, is a small pond artificially increased to a 

 few acres in area by means of a dam. This pond was stocked with carp 

 and bass several years ago. It is fed by two small mountain brooks, 

 and having no other outlet except the sluiceway of the milldam, it 

 furnished an excellent breeding place, in which the fish seemed to 

 thrive well, but during the late summer and autumn of 1899 the fish 

 began to die off in considerable numbers. Their dead bodies were 

 found floating at the surface with no apparent signs of disease or 

 injury, nor did careful and repeated examinations suggest any expla- 

 nation of the epidemic. But the pond contained an abundance of a 

 green floating alga which proved to harbor myriads of small Crustacea, 

 D(fj)/tnia, S!da, etc. 



The devastation continued through the winter, and another visit was 

 made in the spring in the hope of finding some clew. 



This was just at the time suckers were running, and several of them 

 were speared in a pool below the dam. On examining the walls of 

 their gill cavities between 30 and iO specimens of A. catostomi were 

 obtained, many of them with ripe sexual products. These were taken 

 home and kept in aquaria, where the females deposited their eggs, 

 which hatched out a month later into a fine lot of larvae. On showing 

 the adults to the gentleman who owned the pond he said they were 

 found on many of the fish caught, but were never considered speciallj^ 

 harmful. 



He also said that the brooks which fed the pond contained manj^ 

 suckers, most of which were infested with these parasites, a statement 

 afterwards verified. It was determined to try the effect of a concen- 

 tration of the parasites upon a few fish. 



Accordingly 15 or 20 of the Arguli were put in a small aquarium 

 and fish of various kinds from the pond were put in with them. 

 These fish, which included roach, dace, and sun-fish, were put in one 

 at a time, so that the entire number of parasites could concentrate 

 upon each of them separately. 



