LESLIE B. AREY 



fibers, brush fashion, will likewise pick up many glochidia in a 

 minute. 



Experiments were made as follows: 



Two similar strands of twine were spread at thr end into brushes. 

 One was wet with water, the other with N/4 KCl or NaCl and the excess 

 pressed out. Each was then dragged for one minute through dishes 

 containing an equal number of glochidia, and washed gently for thirty 

 seconds to remove larvae enmeshed but not actually attached. Many 

 glochidia were fastened to each brush, but there was no constant or 

 significant difference between the two. 



In so far as this type of experiment is trustworthy, it shows 

 no superiority for an object offering both tactile and chemical 

 stimulation. Yet from the practical side, Howard ('14) states 

 (p. 38) that when ''fish were immersed in a solution of common 

 salt (10 per cent by weight) before placing in the feeding tank, 

 .... it was shown that this treatment had the marked effect 

 of causing rapid infection [of Quadrula ebenus] where previously 

 it had been difficult to obtain. " It will be recalled that somewhat 

 improved responses were obtained when alcohol-fixed, excised 

 gill filaments were first smeared with blood before offering to 

 glochidia (p. 486). A preserved filament alone is, however, in- 

 ferior tactilly to a living one; this difference is doubtless largely 

 a matter of configuration and the physical state of the surface. 



When a gill filament of a fish is excised, the cut surface in- 

 stantly seals off the blood within the vessels and a prompt 

 proliferation of tissue further serves to cover the end. In this 

 way a filament is obtained clean of blood, even without washing. 

 When the tip of such an excised filament is brought between the 

 valves of a glochidium, the larva closes on it, provided actual 

 contact has occurred. There is nothing to indicate a chemical 

 activation or to suggest that ''undoubtedly .... this normal 

 reaction is to chemical stimulation from the ions of protoplasmic 

 salts diffused from the animal fluids of fishes' gills or bodies" 

 (Howard, '14, p. 35). 



Essentially identical results may be obtained with gill filaments 

 first fixed in strong alcohol and thoroughly washed in water. The 

 responses are nearly as ready as with the living gill; the reason 

 for such inferiority as exists is obvious. 



