REPRODUDTION AND ARTIFICIAL PROPAGATION OF FRESH-WATER MUSSELS. 1 63 



In the case of the carp, while the fish is admirably suited to carrying the hooked 

 glochidia of Anodonta and Symphynota , we have never been able to secure a successful 

 infection of the gUls with the hookless glochidia of the genus Lampsilis. The disappear- 

 ance of the hooked glochidia of Anodonta and Symphynota from the gills of the carp 

 may be due to the pulling away of these large and heavy glochidia from the delicate 

 gill filaments, as suggested in our consideration of the survival of the two types of 

 glochidia upon fins and gills, respectively. The disappearance of the hookless glochidia 

 of Lampsilis from both gills and fins of the carp can not be explained in this manner; 

 it suggests rather that there may be some reaction of the host's tissues comparable to the 

 processes which confer immunity against parasitic bacteria in higher vertebrates. With 

 minnows {Notropis cayiiga and N. luirensis) 2 to 4 inches in length, we have not been 

 able to secure any considerable infection with the glochidia of Symphynota complanata, 

 for, although they wUl attach in large numbers during infection, they all drop from the 

 fins and gills within a few days. The fins of these minnows are much more delicate than 

 those of the carp, and the explanation is perhaps that so large a glochidium is easily 

 torn away; but the large-mouth black bass has hardly a delicate fin, and for this fish we 

 have records of infections where no glochidia of 5. complanata became attached during 

 an exposure sufficient for the attachment of many to the gills. In this latter case, the 

 extreme activity of the fish must be considered as a factor which might keep the hooked 

 glochidia from attachment to the fins. 



Darters {Etheostoma ccendeum spectabile) i ^ to 2 inches in length can not be infected 

 successfully with the glochidia of Lampsilis, for although they may fasten so thickly to 

 the fins that many fish die during the first day after their exposure, the surviving fish 

 will slough off considerable portions of the fins and within a week show only the healed 

 and regenerating parts as an indication of their recent experience. The gill slits were so 

 small in these fish that only an occasional glochidium was found upon them. 



Such cases as these are of great importance and should be followed up to determine 

 whether the simple mechanical conditions like over- infection, delicacy of fin, or con- 

 figuration of the mouth parts can give a satisfactory explanation; or whether the histo- 

 logical changes of which the fish is capable, under stimulation by the glochidium, must be 

 regarded as the cause of its immunity. We have not carried out a sufficient number of 

 experiments to feel sure that the simpler explanations can be excluded. In any case, 

 it is interesting that fish like the minnows and darters, which live close to the bottom, 

 are not likely to become heavily infected by some of our most common glochidia. 



BEHAVIOR OF FISHES DURING INFECTION. 



The behavior of the fish during infection is a matter of some importance and has been 

 already mentioned in an incidental manner. The rock bass, large-mouth black bass, 

 and blue-gill sunfish, which are very active and which consequently exhibit powerful 

 respiratory movements, are well adapted to artificial infection, and the proper suspen- 

 sion of the glochidia in the water is secured by the movements of the fish alone. The 

 crappie, which are sluggish and easily killed by handling, require some special device to 



