l6o BULLETIN OF THE BUREAU OF FISHERIES. 



that bacterial or fungus infection sets in. These over-infections sometimes cause such 

 hypertrophy that the fins become swollen and the rays so drawn together that it is 

 impossible for them to spread out normally. Often the fins are raw and bleeding for 

 some days and show red areas within where the blood vessels have become abnormal. 

 The fish are likely to die from this or from the similar injury to their gills, and these 

 over-infections are unsatisfactory if one wishes to bring through their parasitism the 

 maximum number of glochidia. 



The steps in the implantation of the glochidium by an overgrowth of the fish's 

 tissue may be seen in figures 2i and 22, plate ix, and figure 25, plate x. Figures 21, 

 plate IX, and 26, plate x, show the glochidium 3K hours after attachment to the 

 fish's fin. Most of the glochidia have bitten deep enough in from the margin to have 

 a good hold for their hooks. The beginning of the hypertrophy appears as a faint 

 mass of tissue, seen with its nuclei in the detailed figure 26, plate x. At the end of 

 12 hours the overgrowth is well advanced and sometimes, as in figure 27, plate x, shows 

 different stages even in neighboring glochidia. The ragged edge of the host's tissue 

 rises up crater-like about the glochidium, meeting above in a delicate mass, the nuclei 

 of which are shown. Figure 22, plate ix, shows that in 24 hours most of the glochidia 

 are more than half covered, whether upon the edge or the surface of the fins. At the 

 end of 36 hours (fig. 25, pi. x) optimum infections of the carp show all the glochidia 

 which have obtained a proper attachment well embedded, and from this time onward 

 the only change which is visible in whole mounts is a slight increase in the opacity 

 of the cyst, which renders the internal structure of the glochidium less distinct (fig. 23, 

 pi. IX). Some of our infections show embedding in as short a time as 6 hours {Sytn- 

 phynota), and Harms (1909) gives 10 to 12 hours as the time which he observed in 

 Anodonta, so the time given for the figures above referred to is the maximum for hooked 

 glochidia which have been well located. Glochidia upon the fin surface become embed- 

 ded in a similar manner and are then in a very secure position (fig. 22, pi. ix, fig. 25 and 



32,pl. X). 



INFECTIONS WITH HOOKLESS GLOCHIDIA. 



Our experiments in artificial infection with bookless glochidia have been more 

 extensive because this is the type of glochidium found in the species of mussels which 

 are of commercial importance. Species of the genus Lampsilis {ligainentina, recta, 

 anodontoides, ventricosa, subrostraia, and luteola) have been the most frequently used, 

 but infections have also been made with several species of Ouadrida and one of Unio. 

 The list of fishes employed as hosts for bookless glochidia is also more extensive and we 

 are, therefore, able to make statements which we know to be of wider application than 

 those made for the hooked glochidia. 



When the same fish is used, the results for the several species of Lampsilis are 

 very uniform and we can thus discuss the parasitism of this genus as a whole; but we 

 do not find the same mussel giving uniform results with all species of fish. The glochidia 

 of this genus have been used successfully for the infection of blue-gill sunfish (Lepomis 

 pallidus), yellow perch {Perca fiavescens), crappie, large-mouth black bass, rock bass, 



