SCIENTIFIC RESEARCH 253 



before many days unless it is accidentally brought into con- 

 tact with a fish. In this event, it fastens itself upon a fin or 

 gill of the fish, causes a growth of the fish's epithelium and, 

 in the course of a few hours, is completely enclosed within 

 the tissues of its host. Thus securely placed, it undergoes 

 development to a stage in which it is able to assume the life 



FIG. 30. Rock-bass (Ambloplites rupesttis) about five inches in length, infected 

 with glochidia of Lampsilis ligamentina. About 2,500 were successfully 

 carried through the metamorphosis by each fish in this infection. Note 

 the large number on the gills and the small number on fins. (After 

 Lefevre and Curtis.) 



of the parent mussel. It then drops from the fish and takes 

 up an existence upon the bottom which it continues through- 

 out life. Two points are of importance in this cycle. First, 

 the glochidium is a stage at which development ceases and 

 death ensues, unless the larva becomes attached as a parasite 

 upon a fish. Secondly, the gaining of this favorable environ- 

 ment within the fish's tissues is wholly accidental; and so 

 many glochidia perish without so doing, they must be pro- 

 duced in enormous numbers in order that the chances of 

 destruction be overcome and the continuance of the species 

 assured. 



When we examine the paths followed in the establishment 

 of the facts above outlined, it so happens that the trail 



