REPRODUCTION AND ARTIFICIAI^ PROPAGATION OF FRESH-WATER MUSSELS. 1 93 



IX. CONCLUSION. 



Of course, many practical details essential to success will have to be worked out 

 before the artificial propagation of fresh-water mussels will have passed beyond the 

 experimental stage, for the efficiency of the work from an economic point of view will 

 doubtless depend upon the satisfactory solution of certain problems in technique, which, 

 although secondary in character, are nevertheless a prerequisite of success. 



However much is yet to be done — and it should be clear that the work is far from 

 completion — the entire feasibihty of artificial propagation has been demonstrated beyond 

 the shadow of doubt. Besides filling in the gaps, some of them important ones, in the 

 results already obtained, certain fundamental phases of the mussel investigations 

 remain practically untouched. Chief among these is an exhaustive study of the physical 

 conditions of the waters as affecting the growth of mussels: The relation between the 

 mineral content of the water and shell formation; the relation between the character of 

 the bottom, whether rocky, sandy, or muddy, to the habits of diS'erent species; and the 

 relation between the rapidity of current to the life of the mussel and the kind of shell 

 which it secretes. These and many other interesting problems of a similar nature 

 await solution. 



The immense mass of data that have been collected by the Bureau of Fisheries 

 with respect to geographical distribution of species and their relative abundance through- 

 out the Mississippi Valley has not been digested, yet the results which will be derived 

 from a careful analysis of this information will have a fundamental economic bearing 

 upon mussel culture. It is essential to know the centers and limits of distribution of at 

 least the more valuable commercial species for the purpose of effectively conducting 

 the operations in restocking streams and of avoiding useless labor in attempting to 

 establish a species where the chances of its survival would be slight. 



The whole problem of the food of mussels is as yet untouched. Not only are we 

 ignorant of the specific food forms among the micro-organisms upon which mussels 

 depend, but we do not know whether different species, or rather species living under 

 different physical conditions and species possessing different habits, utihze different 

 food forms. The possibihty of artificially rearing cultures of the unicellular organisms 

 used as food — when we know what these forms are — for enriching the water in which 

 young mussels are retained before distribution should be determined, for it is undoubtedly 

 true that results of the greatest practical importance and interest would be derived 

 from such an investigation. 



Very little is known at present respecting the enemies and diseases of fresh-water 

 mussels, yet the importance of information of this nature can not be overestimated. 

 Especially should we know the relative susceptibility of different species to parasitic 

 diseases, and whether certain species are immune against the invasion of parasites 

 which in the case of other forms constitute serious enemies. 



A most fascinating and valuable field of investigation lies open in the study of the 

 causes of pearl formations, for since these concretions are due, in part at least, to the 



