486 LESLIE B. AREY 



played to the same salt. Doubtless there is an additive ionic 

 effect in blood serum. 



Just how blood would be of use in causing glochidia to attach 

 to gills is not clear. Lefevre and Curtis state that they ''lodge 

 among the gill filaments, produce abrasions of the delicate 

 epithelium covering the latter, [and] 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 

 neighborhood of the glochidia .... by exciting vigorous con- 

 tractions of the adductor muscle" brings about attachment. 



Is it true, in the first place, that glochidia, barely of macroscopic 

 size, carried past the gills in the respiratory current, produce 

 'abrasions' sufficient to cause 'hemorrhages,' or 'exudations'? 

 Zoologists who have long studied experimental infection at the 

 Fairport Station state they have never seen corroborative 

 evidence for such a view. It certainly strains the credulity of 

 less experienced observers. Admitting for the moment its 

 reality, how would those light natural infections where few 

 glochidia only may be encountered, be explained? It is, hkewise, 

 debatable whether exuding blood, assuming it were not too 

 rapidly swept away by the relatively large-volumed respiratory 

 current, would not close most glochidia before they were in a posi- 

 tion to attach; there is demanded the combination of a fast- 

 moving glochidium in the exact position to clasp gill tissue and 

 the simultaneous activation of its adductor muscle. I do not 

 believe that this view of excitation by blood, admitting it were 

 based on fact, will commend itself to the reader. That submini- 

 mal concentrations of blood, by dilution in the respiratory cur- 

 rent, would serve to sensitize glochidia appreciably to tactile 

 contact, also finds no support in experimentation (p. 482). 



Theoretically, there are more refined ways in which blood might 

 act. It is found that glochidia clasp a fibrous bit of coagulum 

 avidly. They also attach somewhat more readily to an alcohol- 

 fixed gill filament, which has been washed two days and then 

 smeared with blood or wiped in coagulum, than to a filament 

 similarly treated except for the blood. It might be thought that 



