136 BULLETIN OF THE BUREAU OF FISHERIES. 



of life history at greater length and mth such detail as is necessary to establish an 

 understanding of the conditions necessary for the successful propagation of the various 

 useful mussels and for the effective conservation of the mussel resources. 



HISTORICAL NOTE. 



It seems appropriate to remark that the considerable fund of knowledge which has 

 been gained in very recent years regarding the diversified life histories of fresh-water 

 mussels has been gained very largely as a result of scientific studies which have been 

 stimulated by the practical need of conserving an economic resource, and which have 

 been pursued preliminary to or in connection with the propagation of mussels as a 

 measure of conservation. To put it in another way, the development of the fresh- 

 water pearl-button industry has furnished an effective stimulus to biological studies 

 of high scientific interest and importance, just as the appUcation of science to studies of 

 commercial mussels has rendered a distinct economic service. 



As early as 1695 at least, the glochidium (see text fig. 8, p. 143) was observed in the 

 gills of European mussels, and was understood to be the larval form of the mussel, although 

 it was not then called a glochidium. Of the further stages of life history, science, as well 

 as the public, remained in ignorance for a long time. So wide indeed was the gap of knowl- 

 edge that it became possible for a scientific writer in 1797 to advance the theory that 

 the little mollusks noted in the gill pouches were not young mussels, but were parasites 

 of mussels constituting a genus and species of their own, which the investigator designated 

 with the Latin name Glochidium parasiticum. This view, known as the Glochidium 

 theory, though it never won full acceptance, was strongly supported, and an exhaustive 

 inquiry and report upon the subject by a special committee of the Academy of Sciences 

 in Paris, completed in 1828, failed to effect its decisive defeat. When, however, in 

 1832, Carus was fortunate in observing the passage of the eggs from the ovary of the 

 mussel into the gill pouches, the false theory was definitely overthrown. The name 

 glochidium, suggested though it was by an erroneous assumption, has persisted ever 

 since, being now correctly understood to designate not a distinct animal but a typical 

 stage in the development of the mussels. 



It still remained to determine how and where this peculiar larva became trans- 

 formed into the familiar adult mussel, and this important gap was abridged by Leydig, 

 in 1866, when the glochidium was discovered in parasitic condition upon the fin of a fish. 



The advance in knowledge of the life history of fresh-water mussels made in the 

 ensuing decades was slow and inconspicuous, and textbooks, both American and foreign, 

 continued to reproduce accounts based upon the inadequate observations of the life 

 histories of European mussels. A period of distinct progress came with the extensive 

 and admirable investigations conducted by Lefevre and Curtis (1910, 1910a, and 1912) 

 in association with the Bureau of Fisheries during the years 1905 to 1911. These inves- 

 tigations served to reveal not only some of the distinctive features of the breeding 

 habits and life histories of the American mussels as contrasted with the European 

 species but also the great diversity existing among the many American species, in breed- 

 ing season, period of incubation, and form of glochidia. The results of the investiga- 

 tions aggregated a mass of original observation on various phases of the propagation 

 and life history of fresh-water mussels. Other investigations, notably Ortmann's (191 1, 

 1912, etc.), have contributed materially to knowledge of the breeding characters and 



