. Pearls and pearling . erence in the length of lives ofvarious mussels. Some of the Quadula group probablyrequire ten or .twelve years to reach maturity and thencontinue to live for many years. Some niggerheads have the appearance of being twen-ty-five years old. Some of the Lampsilis group attaina fair size in four or five years. In young shells ofsome varities such as the Lampsilis ventricosus, or pocket-book, and Lampsilis anadontoides, or yellow sand shell,the winter rest periods are very plainly marked. Inmost mussels, however, it is very difficult to determinethe age. The various kinds
. Pearls and pearling . erence in the length of lives ofvarious mussels. Some of the Quadula group probablyrequire ten or .twelve years to reach maturity and thencontinue to live for many years. Some niggerheads have the appearance of being twen-ty-five years old. Some of the Lampsilis group attaina fair size in four or five years. In young shells ofsome varities such as the Lampsilis ventricosus, or pocket-book, and Lampsilis anadontoides, or yellow sand shell,the winter rest periods are very plainly marked. Inmost mussels, however, it is very difficult to determinethe age. The various kinds of mussels have different time,for spawning. Every month in the year is the spawningseason of some variety. After ovulation the eggs passinto portions of the mussels gills which are termed mar-supium. These serve as brood pouches for the retentionand maturity of embryos and glochidia until they leavethe mussel. When the embryos have remained in themarsupium of the mussel for a period of time which 56 Pearls and Pearling. Fig. 6. Lampsilis rectus, or Black Sand Shell mussel plow-ing through the sand or mud at the bottom of a , anal opening; B., branchial opening; F., foot. Arrows indi-cate the direction in which the mussel is moving; alsothe direction of the river current. varies in different kinds of mussels, they gradually passinto the water and are then called glochidia. In the first stages of its development, the mussel livesas a parasite. At the time of spawning the young glochidia fall to thebottom of the river and remain in a helpless condition The Life of the Unio 57 until they die unless they are fortunate enough to becomeattached to a fish on which they pass through post-em-bryonic development as parasites. Multitudes of glochi-dia die by not being attached to the fishes. In most casesthey attach themselves to the gills of fishes, althoughthey also attach to the fins and tails of fishes. There areseveral types of glochidia. One is the hooked typewhich is provid
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