CULTURE OF FRESH-WATER MUSSELS. 75 



Absolutely negative results were obtained from these experiments, as no trace of 

 mussels could be found in screenings from a series of sieves in which the minimum mesh 

 was 2 millimeters. (There is no doubt that the presence of any mussels approaching 

 normal growth of two seasons would have been revealed by this search.) In these ponds 

 normal aeration of the water and sunlight were more certainly provided for than in 

 tanks and aquaria indoors. 



In contrast with these results, largely negative, was a plant of Ouadrula pustulosa, in 

 which the outcome was more satisfactory. In one pond, in its first year used — i. e., the 

 first year the cement was submerged (19 13) — infected fish were placed in the lowest divi- 

 sion — i. e., nearest the outlet and farthest away from the inlet pipe. This division was 

 reserved for channel catfish for the purpose of simplifying the history of this section in 

 case any results were obtained. The pond as a whole was employed as a stock pond. 

 A continuous supply of water was kept up summer and winter with a view to giving 

 any mussels that might be obtained opportunity to reach a size that could readily be 

 found. 



During four years the water was drawn down only a few times. On these occasions 

 the lowering of the water was not allowed to an extent that would be injurious to any 

 mussels that might have started. Only a cursory examination was made for mussels 

 that might have reached a size to be readily detected. Purposely the treatment of this 

 pond was varied from that accorded to the other ponds which, one or two years after 

 plants had been made, were subjected to close inspection by sieving of the bottom soil. 

 Had the same regimen been followed in this case the young mussels would certainly 

 have been found even the first year, and it was an odd chance that the mussels prospered 

 in this one pond where the "let-alone policy" was carried out. As this policy was 

 different from that accorded to all ponds only in respect to the second to fourth years 

 of growth it had no particular bearing upon the question as to how a set was obtained 

 the first year. In seeking an answer to this question we may find a clue by considering 

 wherein the conditions differed from the other ponds. 



In respect to two features, or rather a combination of two (possibly more, of 

 course), the conditions here seem to have been unique for this type of pond. In the 

 first place the division in which the catfish were held was practically free of bottom soil, 

 there being an exceedingly thin layer only, if any, on the cement. In the second place, 

 this division was farthest removed from the intake pipe, around which there was con- 

 siderable subaquatic vegetation, with the result that the water reaching the lower end 

 of the pond was comparatively free of silt which had been unloaded in the upper division. 

 It is pretty certain that juveniles of many species in the earliest stage can not thrive 

 where silt is precipitating rapidly, and it is quite probable that certain species of Nai- 

 ades, like some marine pelecypods, require a clean bottom and possibly a hard substra- 

 tum. It is somewhat difficult to avoid silt precipitation in ponds supplied with water 

 pumped from a turbid river. In this case the form of the pond, the vegetation, and the 

 position of the mussels presumably brought about the result. 



Another probable factor in the successful "set" was the "newness" of the water 

 supply system and the consequent nonestablishment of predacious species which are 

 found under usual pond conditions. Rhabdoccels are abundant in the ponds but not 

 in the river water. Since the reservoir which supplies the ponds was filled first only the 



