618 BULLETIN OF THE BUREAU OF FISHERIES. 
rate of growth, post-embryonic development, and the mutual behavior of 
glochidia, or larve, and fishes as parasites and hosts. 
The results that have already been obtained, although far from being 
complete, will serve as a basis for future investigations, while the lines of attack 
in the main problems have been definitely indicated. We have proceeded far 
enough to make it clear that the ultimate end of the investigation is assured, 
and with proper facilities for the infection and care of large numbers of fish 
the final success of the work is no longer in doubt. ‘The essential facts in the 
life history of the Unionide are known; the general conditions of infection have 
been determined; the entire feasibility of artificially infecting large numbers of 
fish has been established; while the requisite conditions for placing artificial 
propagation on a practical basis are clearly understood. Furthermore, during 
the summers of 1907 and 1908 several parties, working under the direction of 
the Bureau of Fisheries, have made extensive observations on a number of 
different rivers in the upper Mississippi Valley, with a view to determining the 
distribution of all of the species of mussels occurring in these waters. The 
rivers that have been explored in this manner are the upper Mississippi, Illinois, 
Iowa, Minnesota, Wabash, Ohio, and Tippecanoe, as well as several smaller 
streams in Indiana. When the results obtained by these parties have been 
brought together, we should be in possession of detailed information regarding 
the distribution and relative abundance of at least all of the important com- 
mercial species throughout this region. In addition, the breeding seasons of 
almost all of the important commercial species have been determined, and a 
large mass of miscellaneous data relating to a great variety of subjects has 
been accumulated. 
Some of the more important results that have thus far been obtained in 
the investigations are briefly presented here. 
SOME FACTS IN THE REPRODUCTION AND LIFE HISTORY OF MUSSELS. 
As is well known, the Unionide carry their young in the gills, which act 
as a marsupium or brood chamber until the completion of the embryonic 
development. The eggs are passed from the ovaries into the suprabranchial 
chambers, where they are fertilized by spermatozoa brought in by the inhalent 
current of water. In many species the eggs are bound together in masses by a 
gelatinous or glutinous matrix which is secreted by the gills and which may be 
very tenacious. ‘This, however, in most cases gradually dissolves away as 
development proceeds, until at the close of the embryonic period the larve or 
glochidia are no longer agglutinated. These masses assume in different species 
many forms of flat plates or cylindrical cords which fill the water tubes of 
the gills. The latter may be greatly distended or modified in various ways 
to receive the egg-masses. In some species, on the other hand, the condition 
