644 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvii. 



ino- disks and also opposite the base of the tirst swimming legs in the 

 lateral lobes. 



The rest of the surface is filled in with orange-j'ellow of varying 

 intensity, the posterior portion of the carapace lobes ))eing tinged 

 with brown, while the side branches of the stomach give more or less 

 of a reddish hue to the parts overlying them. 



Through this variegated groundwork the ribs, the digestive tube, 

 and the reproductive organs stand out prominently. The ribs are a 

 bright golden orange, the two central longitudinal ones being bor- 

 dered with yellow green. 



The digestive tube, when the parasite has taken a full meal, is deep 

 wine red in the carapace and thorax, but fades to a green-yellow in the 

 abdomen. It has a dark-green border on either side which occupies 

 all the thoracic segments outside the intestine itself and extends forward 

 anteriorly to the frontal border and posteriorly to the extreme tip of 

 the abdomen lobes. 



The testes and semen receptacles are a rich purj^le-red, so deep as to 

 be almost opaque. 



The e3'es and brain are large and of a ))rilliaut black. 



With such a rich variety of color it would be natural to suppose that 

 these copepods would fade quickly in preservatives, but such is not the 

 case. After being hardened in chrome-acetic, corrosive-acetic, and 

 Peren^'i's, they have been kept nearlj^ three years in alcohol with so 

 little change as hardly to be distinguished from fresh specimens. 

 The}' can also be run up through the alcohols, cleared inxjiol or clove 

 oil, and mounted in balsam without change of color. Indeed, eau-de- 

 javelle is the only agent yet tried which will bleach the color. This 

 removes it entirely and leaves the Arguhis perfectly transparent. 



Thus far the species has been found only upon the common pickerel 

 {Lucius reticulatus Le Sueur), but is likely to be found upon other iish 

 also at the breeding season. 



Actual experiment has proved that they are capable of living on red- 

 fin shiners, bream, etc., for a long time." 



This single host is, however, very widely distributed throughout the 

 United States, and in all probability the parasite has an equal distribu- 

 tion. Not more than two or three specimens are found upon a single 

 fish, and these are always in the gill cavity. Often also it is necessar}' 

 to examine fifteen or twenty fish before finding a single parasite, so 

 that they could be easilj^ overlooked and a good summer catch of fish 

 might not reveal their presence. For this reason winter is the best 

 time to secure them upon fish caught through the ice, and as they 

 remain alive for some time after the fish is dead an entire da^-'s catch 

 can ])e looked over. In this manner as many as thirty have been 

 obtained in a single afternoon from three adjacent ponds. Thus far 



«Proc. U. S. Nat. Mus., XXY, 1902, p. 647. 



