COPEPOD PARASITES AND MUSSEL GLOCHIDIA ON FRESH-WATER FISHES. 343 



II. Is there any fellowship between the different species of the two kinds of parasites'? 

 Do we find certain species of qlochidia associated with the same copepod tn a majority of 

 instance sf 



This question can also be answered by reference to the table (p. 338), from which 

 we deduce the following: 



1. Of the external-fin glochidia Anodonta corpulenta is by far the most widely dis- 

 tributed and is alwaj^s accompanied by an external Argulus parasite, usually A. appen- 

 di-culosus. The green sunfish, the calico bass, and the skipjack are apparent exceptions; 

 Anodonta glochidia have been found upon them but no Argultis copepod. It must be 

 remembered, however, that the glochidia are fastened in the fins and remain there no 

 matter how long the fish may have been kept or how much it may have been handled. 

 On the other hand, the copepod merely clings to the outside surface of the fish and is 

 easily brushed off when alive and practically always falls off when dead. Only a few 

 of these fish have been examined under conditions favorable for finding the copepods, 

 while the conditions are always favorable for finding glochidia. 



Such being the case, it seems reasonable to expect that an Argulus parasite will 

 be found upon the three fish just mentioned as the result of future examination; but 

 the argument ought to work equally well in the opposite direction, and hence we may 

 look for the future discovery of the glochidia of A. corpulenta upon the channel cat, its 

 copepod fellow having been already found. 



2. The glochidia found upon the gills of fish may be di\dded into the two great 

 groups of Lampsilis species and Quadrula species. Accompanying the former we find 

 Ergasilus ccertdeus in every instance, except upon the largemouth black bass, where it 

 is replaced by Ergasilus nigritus, one of the new species. Accompanying the Quadrulas 

 we find Ergasilus versicolor upon the catfishes and the skipjack and Ergasilus centrarchi- 

 darum upon the Centrarchidae. In this instance the copepods and glochidia are equally 

 well protected, and the only hindrance to their discovery is the lack of fish specimens. 

 Some species of fish are always scarce, while others that may be ordinarily plentiful 

 may be scarce at just the time when they are likely to become infested with the copepods 

 or the glochidia. Hence, while one of the parasites might be well known upon the fish, 

 the other might have escaped notice. 



Apparently something of this sort has happened to a few of the catfishes and Cen- 

 trarchidse; copepods have been found upon them repeatedly, but thus far no mussel 

 glochidia have been discovered. It would seem reasonable, however, to expect them, 

 and some species of Quadrula will probably be found in the future upon the yellow cat, 

 the bullhead, and the Fulton cat, while some species of Lampsilis will be found upon 

 the common sunfish, Eupomotis gibbosus, the warmouth bass, and the smallmouth black 

 bass." 



In connection with the association between E. centrarchidarum and Quadrula 

 glochidia the following may be suggested : 



(o) E. centrarchidarum is found on the gills of the largemouth black bass, but it is 

 accompanied by E. nigritus, one of the new species which evidently takes the place on 

 this host of E. cceruleus, the regular associate of Lampsilis species. The presence of 

 centrarchidarum, therefore, is not to be interpreted as indicating that it is here excep- 



o Since the writias of this paper two species of Lampsilis glochidia have been discovered upon the gills of the warmouth 

 bass and have been inserted in the table on page 338. 



