CULTURE OF FRESH-WATER MUSSELS. 8 1 



the movements of which become gradually more vigorous until this remarkably motile 

 organ sweeps an arc in the plane of the valves included by the three sides of the mantle 

 cavity (the anterior, posterior, and ventral opening of the shell). 



The cases observed by the author took several hours, but under the conditions of 

 observation the difficulties are greater than when normal in the living host. There seems 

 to be an adhesion of the shell to the host's excised tissues that is due, very likely, to 

 coagulation. In some cases the process was so prolonged that, before escape was effected, 

 considerable decomposition of the host tissue was apparent. The juveniles, therefore, 

 exhibited a remarkable resistance to the products of decay toxic to most animals. 



The free juvenile under conditions of observation appears at times very active. 

 In moving from place to place the foot is extended a distance fully equal to the length 

 of the shell, becomes fast to the glass or some object, then contracts, bringing up the 

 remainder of the animal. This is repeated again and again, thus accomplishing a kind 

 of creeping motion which carries the small organism across the field of the microscope 

 in a suprisingly rapid manner. The presence of cilia all in rapid motion upon the foot 

 and edges of the mantle add to the effect of vigorous vitality. 



It seems probable that the young mussels do not move about much if they find a 

 suitable bottom. Time and again the author has looked for them on trays set on the 

 bottom of the aquarium to catch them as they fall from the hosts, but all in vain before 

 washing off the sediment. When this accumulated sediment in which they were lying 

 was removed, they could be seen, and after being left for a few minutes without dis- 

 turbance the}- would extend the foot and begin the migration reactions mentioned 

 above. Often one finds considerable debris adhering to their shells. In one species 

 delicate hair-like processes were observed. A covering of bottom sediment doubtless 

 serves as a shield from enemies. 



The mortality at this age is very high as may be seen by the number of empty shells 

 and the scarcity of live mussels a few days after the beginning of free life. Their chief 

 enemies, so far as noted under cultural conditions, are very small rhabdoccels, turbel- 

 larians that are extremely abundant during the summer in the water as it comes from 

 the reservoir. These swarm over the bottom of the aquaria, and examples may readilv 

 be found through the transparent body walls of which may be seen the mussels they 

 have eaten. These have been observed in both the glochidial and early juvenile stages. 



The species of Turbellaria as determined by Caroline Stringer were Microstomum 

 sp., Stenostomum leucops, and 5. tenuicauda. Specimens of the Microstomum were 

 preserved with the young mussels still inclosed in their relatively capacious intestines. 

 Another enemy which it has been possible "to arrest with the goods still on him" is a 

 small chaetopod, apparently Chaetogaster. Neither of these worms is more than 0.4 

 millimeter wide, so that after the mussel attains three weeks' growth it must be safe from 

 their ravages. 



The food of the very young juveniles seems to be similar to that of the adult; i. e., 

 at least in part, microscopic plants and animalcules taken in through the incurrent 

 siphonal aperture. In small juveniles one can watch these as they enter. The author 

 once observed a considerable deposit of excreta containing the skeletal remains of such 

 forms as diatoms. This debris was lying in a heap outside beneath the excurrent siphonal 

 opening. 



