154 BULIvETIN OF THE BUREAU OF FISHERIES. 



of diminishing intensity, the snapping occurred intermittently for from lo to 50 seconds. 

 Here the contractions were quite rapid at first, one or two every second, but soon the 

 intervals became longer, until finally the activity was ended by the closure of the valves. 

 In some cases it was observed that after the first few snaps the muscle did not completely 

 relax, and each subsequent contraction caused the valves to describe a shorter arc. This 

 experiment was repeated time and time again, with invariably the same result, and it 

 was astonishing to see what a small quantity of the fish's blood was required to produce 

 the reaction. It should be emphasized, furthermore, that after the stimulus had caused 

 the final contraction of the muscle the valves remained permanently closed. 



The experiment was later performed a great many times with the glochidia of Lamp- 

 silis ligamentina and subrosirata, and identically the same reaction was obtained with 

 the blood of several different fishes and that of the frog, Necturus, and man. 



Since the hookless glochidia, which are essentially gill parasites and, when taken 

 into the mouth of the fish lodge among the gill filaments, produce abrasions of the 

 delicate epithelium covering the latter, a more or less extensive hemorrhage from the 

 blood capillaries occurs, as may be readily seen from a microscopic examination. It is 

 therefore evident that blood exuding from the gill filaments in the immediate neighbor- 

 hood of the glochidia must have the same effect as in our experiments, and, by exciting 

 vigorous contractions of the adductor muscle, furnish an efficient stimulus in bringing 

 about a firm and permanent attachment to the filaments. It is true that hookless 

 glochidia will occasionally secure an attachment to the edge of the fins and other exter- 

 nal parts of the fish, but it is quite evident that they are not adapted to such locations, 

 as they rarely succeed in remaining there. It is possible that when they do become 

 attached to the fins the closure of the valves is due to the presence of blood on the latter; 

 but, since hookless glochidia occasionally close when touched repeatedly, the attach- 

 ment in these situations is probably brought about by a sluggish response to contact 

 with the edges of the fins. Their characteristic place of attachment, however, is the 

 gill filaments, and this definite reaction to the fish's blood constitutes a most striking 

 functional adaptation to the special habit of hookless glochidia as gill parasites. 



Although the matter has not been exhaustively studied, it is in all probability the 

 salts of the blood that are responsible for these reactions. A series of experiments, 

 however, has been undertaken for the purpose of determining the reactions of glochidia 

 of this type to solutions of several different salts, and, although the investigation has 

 not yet been completed, a brief statement may be made here. Diluted sea water and 

 solutions varying in strength from 0.5 to i per cent of NaCl, KCl, KNO3, and NH^Cl 

 have exactly the same effect as fish's blood, although the intensity of the reaction varies 

 somewhat in certain cases. Weak solutions of MgClj and MgSO^, however, as would 

 be expected, inhibit contractions, and glochidia, after treatment with these salts, may 

 be killed in an expanded condition, if allowed to remain in the solutions for a sufficient 

 length of time. 



