66 COMPARATIVE ANATOMY 



the edges of the mantle. The Glochidia, when a fish is in their 

 neighbourhood, rapidly open and close their valves, and some 

 have the luck to attach themselves to a fish by the sticky byssus 

 thread and then fix themselves to the gills, fins, or tail by their 

 hooked valves. They become imbedded in the integument of 



Fig. 15 



Two views of the glochidium larva oi Anodonta, after Schierholtz. A, from the 

 side ; B, from below, a^a-t bunches of seta; ; ad, the single adductor muscle ; 

 by, byssus ; k,k, hooks on the valves of the shell : //, lateral pits ; sk, shell ; 

 st, stomodseal invagination ; vg, visceral ganglion. 



the fish and remain as parasites on it for several weeks, during 

 which time they undergo further development. The foot is 

 formed as an outgrowth behind the mouth, and the gills are 

 developed as a series of finger-like outgrowths on each side 

 of and somewhat behind the foot. The larval adductor 



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