GLOCHIDIA — FACTOES UNDERLYING ENCYSTMENT 487 



as glochidia bite into the gill tissue there would be a slight oozing 

 about the rim of the valves, and that this fluid, spreading and 

 coagulating on the adjacent epithelium, induces attachment 

 chemically. Avoiding the question as to how the first larvae 

 would gain attachment, the remainder of the supposition is not 

 borne out by direct observation, not even when the valves com- 

 press, and sink into, gill tissue which includes a blood vessel. 



It would appear that the tactile sensibility of glochidia is 

 adequate to insure encystment. A chemical responsiveness is 

 likewise highly developed, possibly because the organs of sensory 

 reception are of a 'general' type (Arey, '18; but note the evidence 

 for the direct stimulation of muscle, p. 482), yet the organism 

 makes little use of it. To state dogmatically that a chemical 

 response is not utilized during or after attachment, is, perhaps, 

 hazardous. At least, on the basis of observation, it may be said 

 that the facts can be explained satisfactorily on a tactile basis, 

 and that if there is any chemical perception operative it is not 

 through distance receptors (p. 488). 



The results of quantitative studies on chemical activation may 

 prove to be directly applicable in propagative work. At present 

 the physiological fitness of glochidia is tested by adding crystals 

 of common salt to a sample of larvae. The resulting solution is 

 relatively of high concentration. It would be far more rational 

 to test this sensitivity to an active salt, such as KCl, at appropri- 

 ate limiting concentrations; thus for Lampsilis luteola (and 

 perhaps for the mucket group, or even the Lampsilis class?) 

 samples which close promptly in N/100 KCl (p. 481) would be 

 sufficiently 'ripe' and 'active.' To what extent such procedure 

 is practical or advisable, only experimentation can decide; 

 theoretically, it promises much. 



IV. THE MECHANISM OF ENCYSTMENT 



That the tactile response is adequate to insure the attachment 

 of bookless, as well as of hooked glochidia, is a statement amen- 

 able to proof. A hair moved about at random in a watch-glass 

 containing glochidia will after a time have several larvae fastened 

 to it. A thread or strand of twine separated into its component 



