REPRODUCTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. l6l 



the red-spotted sunfish {Lepomis humilis), and the green simfish {Apomotis cyanellus). 

 As with the hooked glochidia, the infections have all been made upon fish under 6 inches 

 in length, upon which these glochidia remain in numbers only on the gill filaments, 

 although during infection some may become attached to and even embedded upon fins 

 and other external parts. Harms (1908) concludes that the bookless type persists in 

 much greater numbers on the fins of small than of large fish, and that the hooked type 

 will survive upon the gills if large fish are used. It is doubtless true that the size of 

 the gills and fins is an important factor in determining the place of attachment for 

 each type, since the bookless form is better adapted for holding to a delicate surface 

 like a gill filament or a fine fin, while the hooked type seems likely to be easily torn 

 from such a surface. When the bookless form does once become established upon an 



Fic. 2. — Rock-bass {Ambloplites rupeslris) infected with clochidia of Lampsilis ligamentina. About 2.500 were succc&sfuUy 

 carried through the metamorphosis by each fish in this infection. Note the large number on the gills. 



external part, it will develop there without mishap, as shown by the figure of a hooked 

 and a bookless glochidium developing side by side upon the margin of a fin (fig. 29, 

 pi. x). Within the mouth cavity these glochidia become attached to the gill bars and 

 rakers, if these parts are covered by a sufficiently delicate epithelium, though they are 

 always found in the greatest numbers upon the gill filaments. In most of our infec- 

 tions the filaments are more heavily infected toward their outer ends (fig. 43, pi. xi), 

 the distribution varying somewhat with the species of fish. For example, successful 

 infections of rock bass with Lampsilis ligamentina show about seven glochidia upon 

 the distal third of the filament to one upon the proximal two-thirds; of large-mouth 

 black bass about 3 to i, and of yellow perch about 1% to i — differences which are 

 probably due to some particular configuration of the mouth parts, which causes the 

 glochidia to fall more upon one region of the filaments than another. 



