The Shell-Collector’s Handbook. 29 
opens on the exterior of the body just below the 
orifice of the ureter. In the female, however, the ova 
do not pass directly out of the body, but congregate 
in large numbers between the two lamelle of the 
outer gill where they develop into peculiar larval 
forms—which at one time were considered parasites 
of the mussel—known as Glochidia. Each valve of a 
Glochidium-shell is shaped like an _ equilaterial 
triangle, with the apex incurved and produced into a 
sharp saw-edged tooth. A single adductor muscle is 
present ; the foot is small and slightly developed, and 
in its place two filaments—the byssal jfilaments—are 
seen projecting from the larva. 
In this form the embryo is ejected from the gill of 
its brood-mother into the water. Then sinking down 
to the bottom of the pond the shell gapes widely, for 
the single adductor muscle is not strong enough to 
keep the valves together. Swimming by the flapping 
of its valves, when it becomes a little more developed, 
the young Anodon attaches itself by means of its 
byssal filaments to either the gill-covers, lips, or fins 
of a fish—especially Leuciscus and Gobio—and fixes 
its sharp teeth into its body. Remaining for a time 
in this parasitic condition, the single adductor muscle 
and the byssal threads atrophy, and in their place the 
anterior and posterior adductors become developed, 
and the foot more developed. Changes goon until the 
larva has become like the parent from which it 
originated, and then the young Anodon loses its hold, 
drops down into the bottom of the water in which it 
exists, and commences the every-day life of its mother. 
KEFERSTEIN’s ANALOGY.—Keferstein has compared 
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