grier] THE FRESH WATER PEARL MAKERS 341 



Most remarkable organs are the gills, for in the outer two, and 

 sometimes in all four,, are deposited the eggs by the parent animal. 

 Here they undergo the first stages of development and transform 

 into minute creatures termed glochidte, possessing a bivavle shell 

 beset with teeth. After a time, they are discharged, either through 

 the exhalant siphon or small holes in the edge of the gills. The 

 glochidia are able to open and close their shells rapidly when in the 

 least disturbed, and this may result in their attachment to the fins 

 or gills of some passing fish— an occurrence necessary for their 

 further development. Shortly they become embedded in the flesh 

 of their host, and although their exact relations are not understood, 

 in a few weeks they "undergo a wonderful series of changes," 

 resulting in the production of a small mussel. The latter soon 

 breaks through the thin skin of the fish and drops to the bottom, 

 setting up in business for itself. After a growth period of five 

 years it may attain its mature size, and thereafter may live 30 

 years or more. 



Frequently mussels are found discharging their young during the 

 summer months. Each little animal is but one of thousands of. 

 white specks surrounded by a gelatinous material. The interesting 

 thing about the process as it has been described, is that each kind 

 of mussel has its own kind of fish host, and if such is not found, the 

 little animal perishes in two or three days. We thus rarely find a 

 variety of mussels in streams not possessing a variety of fish and 

 some of our most worthless fish from an edible standpoint, i. e. the 

 gars, are invaluable because they, and they alone can carry with 

 them the young of mussels whose shell possesses an economic value. 

 The shells of the few kinds which can develop independently of the 

 fish are worthless commercially. 



The foot is usually of a yellowish white color and of a tough 

 muscular consistency. It probably presents the greatest obstacle 

 to the utilization of the fresh water mussels for food, since this 

 structure does not attain comparatively such a development in 

 most of the edible marine bivalves. By means of the foot, the 

 animal leisurely ploughs its way through the mud as indicated in the 

 illustration, and if a mussel be taken out of water, the foot is seen 

 to slowly contract and be withdrawn steadily into the shell. It is 

 also of use as a burrowing organ which enables the animal to sink 

 deeper in the moist mud in time of drought, or raising it when over- 

 whelmed with the suffocating mud of the spring freshets. 



