GLOCHIDIA — FACTORS UNDERLYING ENCYSTMENT 479 



E. Chemical excitation 



The valves of a glochidium close in response to various chemical 

 solutions. A common method of testing the ripeness of glochidia 

 and their fitness for propagative infections is to add crystals of 

 table salt to a sample of larvae and observe its effect. From 

 observations on the action of blood and a few commoner salts, 

 Lefevre and Curtis ('12) reported a closing response in both 

 hooked and bookless forms. Since they believed the tactile 

 sensitivity of bookless glochidia inadequate to cause attachment, 

 it was assumed that the response in this group is at bottom 

 chemical, induced by hemorrhages from abraded gill tissue. This 

 view will receive attention on a later page (p. 486). 



The method of procedure followed in these determinations was 

 to place 50 to 100 active larvae on a slide in a water film just 

 sufficient to allow their separation. They were then so flooded 

 with the proper solution that the original water did not materially 

 affect the final concentration. The limiting concentration ad- 

 equate to produce responses and the promptness of the reaction 

 at the lower dilutions furnished the criteria for comparisons. 



1. Hookiess glochidia. As in the other experimentation, the 

 most intensive tests were made on the large glochidium of Lamp- 

 silis luteola. First, the range of chemical sensitivity was sought 

 with a variety of reagents, and next, certain critical quantitative 

 data. 



Acids 

 HCl: 



N/2 and N/25. All glochidia close at once. 



N/100. All, or nearly all, close. 



N/250. A few only respond. 

 Acetic acid: 



M/25. All close but the response lags. 



M/50. Same. 



M/100. Relatively few affected. 



The inferior stimulative power of acetic, as a type of organic acid, is 

 well known. 

 Picric acid: 



M/10. Most close at once; others only after a definite latent period. 

 Closure may be quick, or slow and deliberate. 



