Howard. — Glochidia Infection on River Herding 99 



velopment in this time indicates that the period of meta- 

 morphosis is not of exceptional length. 



The clear globular cysts observed in infections on the 

 herring are due to structural peculiarities of the gill, 

 modified by cyst formation, rather than to migration of 

 the parasite. 



Taking into account the present scarcity of the River- 

 Herring in rivers where it was formerly abundant, it 

 would seem practicable only to attempt propagation 

 where fish and mussel are abundant. This and other con- 

 siderations would warrant a reiteration of the views 

 advanced by the author in 1913 (Howard, 1914a). "The 

 remarkably full infection of this species in nature indi- 

 cates that under natural conditions propagation of the 

 mussel will take care of itself. Thus recommendation 

 of measures for preventing the extermination of the nig- 

 gerhead mussel would be along the line of protection of 

 the herring as the host fish. The cause for the increasing 

 scarcity of the herring seems not to be due to capture in 

 large numbers as the fish is not commonly used for food 

 throughout its range. It is more probable that it is due 

 to artificial conditions, such as the obstruction of its nat- 

 ural migrations by dams, and the introduction into the 

 rivers of injurious wastes from manufacturing plants, 

 etc." 



Without a more exact knowledge of its present status, 

 we can not say how far these things affect this species. 

 We must look with interest for studies upon the occur- 

 ence of this fish, its migration and breeding; in fact, a 

 knowledge of its whole natural history is required, for 

 though not itself esteemed, on it depends the niggerhead 

 mussel and the welfare of an important industry. 



LITERATURE CITED. 



Howard, A. D. : 



1912. The catfish as a host for fresh-water mussels. Read at the 

 Denver meeting of the American Fisheries Society, September, 

 1912. Transactions American Fisheries Society. 



1914a. Experiments in propagation of fresh-water mussels of the 

 Quadrula group. Appendix to report of U. S. Commissioner 



