t»IlOGRESS IN BIOLOGICAL INQUIRIES, 192S. 19 



at once in natural waters, and, second, to learn how to rear juvenile 

 mussels from infected fish kept in confinement, with greater con- 

 sistency in results, higher percentages of survival, and more rapid 

 growth and, correspondingly, with greater economy. During recent 

 years notable progress has been made at the station and in its field 

 work in the rearing of young mussels from artificial infections, a 

 task that had previously baffled all attempts. The results obtained 

 from experiments up to the present time have not, however, been 

 so consistent or interpretable as to justify the immediate recom- 

 mendation of this type of. mussel culture as a practical venture, 

 although they are such as to give encouragement to the continuation 

 of the experiments. In one experiment during the past fiscal year a 

 survival of 81.5 per cent was obtained, a figure more than 10 times 

 higher than is deemed necessary in ordinary mussel propagation to 

 justify the practical economy of the operations in natural waters. On 

 the other hand, in some experiments where all known conditions are 

 supplied to yield substantial results the rate of survival is insignifi- 

 cant. Undiscovered factors are evidently involved. At this stage it 

 would be folly either to desist from further trials or to fail to in- 

 quire as exhaustively as is practicable into the behavior and physi- 

 ology of the young mussel and into the intricate environmental fac- 

 tors to which the mussels are subjected in the stages just following 

 parasitism. Single factors must be tested out wherever it appears 

 necessary and practicable. Among the studies of this nature that 

 have been pursued during the past year the following may be men- 

 tioned : 



Dr. E. P. Churchill, temporary investigator, made a study of the 

 food and feeding habits of fresh-water mussels with special refer- 

 ence to juveniles. The facts were apparently established that in the 

 ingestion of w^ater-borne materials there is no choice of food par- 

 ticles from other substances, the ingestion of a particle brought to 

 the mouth depending in a large measure upon mechanical factors, 

 the size, shape, or position of the particle. Useless materials such 

 as carmine, sand, and earth are taken into the stomach in quantities 

 evidently proportional to the abundance of the materials in suspen- 

 sion in the water, but the excessive predominance of nonfood mate- 

 rials may be seriously detrimental to the oyster either by occupying 

 too much space in the alimentary canal or by causing the diver- 

 sion of materials from the mouth and thus checking the feeding 

 activity. This is in accord with the results of some previous in- 

 vestigators dealing with other species of bivalve mollusks. Minute 

 animals (Protozoa) as well as plants are ingested in quantities and 

 presumably utilized. In the young mussels, at least, material passes 

 through the alimentary canal in from two to five hours, usually in 

 three. Foul conditions of the water may prevent mussels from open- 

 ing and feeding. 



Dr. A. D. Howard and B. J. Anson, working together, and.C. N. 

 Blystad have given attention to the biological and phvsical condi- 

 tions affecting survival of the juvenile mussels, considering such 

 factors as the free oxygen and carbon dioxide content of the water, 

 silt in suspension or sedimentation, current at bottom, light, char- 

 acter of bottom, enemies (worms, insect larvae, and snails), crowding 

 of mussels, and unfavorable plant growtlis. It has been ascertained 



