SCIENTIFIC RESEARCH 255 



made the somewhat accidental observation of glochidia 

 living as parasites upon fishes, was the clew discovered and 

 the work of following the later stages made possible. 7 During 

 this final period, the post-glochidial development became 

 well known and the earliest stages of egg and embryo were 

 reexamined in the interests of fundamental research upon 

 development. Most significant of all in illustration of the 

 importance of abstract research, is the fact that from 

 Leeuwenhoek's beginning, all this work was part of an attempt 

 to understand the nature of individual development. It was in 

 no sense directed toward utilitarian ends. Originally, it was 

 a question of the mode of generation, whether spontaneous or 

 by eggs and sperms. Later, it became a question of compar- 

 ative embryology and the tracing of each organ in the body 

 back to the cell or group of cells from which it originated. 

 Through it all, the direct pressure of utilitarian considera- 

 tions is nowhere to be found; but rather a belief by the in- 

 vestigators that the facts were worth knowing, because they 

 gave a broader horizon to the landscape of nature. 



In 1891 the first pearl button was cut from a fresh- water 

 mussel shell. The business soon became a substantial 

 industry and within ten years the destruction of the mussel 

 beds in the Mississippi River seemed imminent. At the 

 request of the manufacturers, the United States Bureau of 

 Fisheries undertook a brief survey and offered some whole- 

 some advice, all of which was disregarded with the opening 

 of new sources of supply in Arkansas, Indiana, and along the 

 Ohio. Seven years later, under the stress of a still diminish- 

 ing supply, the manufacturers again approached the Bureau 

 of Fisheries, with the result that the Bureau made an ex- 

 tensive study of the mussel, having in view its artificial 

 propagation. The results of this investigation have been 

 brought together ; 8 and, since there are still many f unda- 



7 Leydig, F., " Mittheilung iiber den Parasitismus junger Unioniden an 

 Fischen in Noll." Tubingen, Inaug, Dis. Frankfort a. M., 1866. 



8 Lefevre ; G-, and Curtis, W. C, " Studies on the Reproduction and Artifi- 



