344 BULLETIN OF THE BUREAU OF FISHERIES. 



tionally associated with Lampsilis species but, rather, that Quadrula glochidia will be 

 found in the future upon this fish as they have been upon so many of the sunfishes and 

 basses other than the largemouth. 



(6) Upon the sunfishes it is worth noticing that the two copepods ccernleus and 

 cenirarchidarum occur together, and we should expect such fish to become the natural 

 hosts of both Lampsilis and Quadrida glochidia. Two of them, the bluegill and the 

 green sunfish, have already yielded both kinds of glochidia, and it would seem probable 

 that future investigation will find both kinds upon the other sunfish where now there 

 is but a single kind. 



(c) E. centrarchidarum is found upon the gills of the wall-eye, which have thus far 

 yielded only Lampsilis glochidia; but upon the sauger, another fish of the same genus 

 as the wall-eye, both kinds of copepods and both kinds of glochidia appear. Further- 

 more, both fishes yield the same species of Argulus, so that it does not seem presumptive 

 to suppose that the second species of Ergasilus and Quadrula glochidia will eventually 

 be found upon the wall-eye, as they have already been upon the sauger. 



3. There is a single well-marked instance of individual association between a 

 glochidium and a copepod. Lampsilis anodonloides, whose glochidia are practically con- 

 fined to the gars, is found to be accompanied by a peculiar copepod, Ergasilus elegans, 

 another new species, which differs markedly from the others of its genus in the fact 

 that the female remains free swimming for a much longer period. Indeed, it seems 

 probable that they leave the fish's gills after having fastened to them and swim about 

 freely. There are two other new species, Ergasilus lanceolaius from the gizzard shad 

 and E. elongatus from the spoonbill cat, which are fully as peculiar as E. elegans and 

 which may well be the copepod half of other individual associations whose glochidial half 

 has not yet appeared. Furthermore, we may look for E. elegans upon the alligator gar, 

 whose gills have already yielded specimens of Lampsilis anodonloides. 



4. It has long been known that certain species of copepods are confined to particular 

 hosts and are not found upon any others. The table furnishes us several well-marked 

 examples of this: Argulus mississippiensis and A. ingens are each found upon a single 

 host, and although the two hosts are gars and very closely related to each other the 

 copepods are distinct species. Again, the two species of Ergasilus just mentioned, 

 namely, lanceolaius and elongatus, are each restricted to a single kind of fish and are not 

 likely to be found elsewhere. The same is true of Ergasilus mcgaceros and of Salmincola 

 oquassa and S. edwardsii; in fact, a good proportion of copepod parasites of both fresh- 

 water and salt-water fish show such restrictions. 



When we look at the glochidia we find that there are fully as many of them confined 

 to a single host. Lampsilis alata, gracilis, and purpuraia, and Quadrula solida, ebcnus, 

 and trigona are good examples. Probably further investigations will modifj' many of 

 these as well as of the copepods, but it is equally probable that some of them will prove 

 to be always solitary. In the case of the glochidia we are not compelled to wait for 

 natural infections, for we can subject a fish to the glochidia of many mussels and deter- 

 mine experimentally whether or not it will make a suitable host for them. In fact, 

 this has been done by Dr. A. D. Howard, who, in the Bureau of Fisheries document 

 no. 801, calls attention on page 36 to what he calls "Restricted infection," which 

 he has demonstrated by actual experiment in the case of Quadrula puslulosa upon the 

 channel cat. 



