478 LESLIE B. AREY 



stantiate this. That protoplasmic activity should be correlated 

 with temperature is in accord with general experience in animal 

 conduct. 



It is found in experimental propagative work that cold weather 

 infections are not so successful as summer ones. Dr. A. D. 

 Howard informs me that in winter he was unable to obtain an 

 infection with Lampsilis anodontoides on the gar until the water 

 was warmed. According to Dr. F. H. Reuling, summer in- 

 fections are gained at 75°F. with obviously greater ease than, 

 for example, at 65°F.; probably the explanation for this lies 

 wholly in the variable respiration rate of fishes due to tempera- 

 ture. In extremely cold weather the decreased activity of the 

 glochidia doubtless is a factor as well, yet some larvae which 

 mature during the winter are notably active (p. 476). 



D. Other modes of excitation 



Glochidia, being non-motile, cannot express a response to such 

 sources of stimulation as gravity, currents, and ordinary surface 

 contact. Their common position on the bottom with gaping 

 valves directed upward is of use to those that attach to fins and 

 other external surfaces. The assumption of such an advanta- 

 geous orientation is purely mechanical, due to the curvature of 

 the open valves and tlie distribution of body mass.^ It is ob- 

 served sometimes that salt crystals introduced into a dish of 

 glochidia cause those near the limits of the sphere of influence to 

 partially contract, or 'wink,' several times before closing. This 

 I have never observed with solution of salts. It seems probable 

 that such a phenomenon is dependent on lines of diffusion ex- 

 tending from the salt crystals which for a time stimulate the 

 glochidium unequally. 



^ It may be noted here that the valves of glochidia of Anodonta corpulenta are 

 maximally opened to 180°; this results in the larvae's assuming positions with the 

 valves directed either up or down. 



