472 LESLIE B. AREY 



death of the larva. Even glochidia, closed by a quick jab of the 

 hair, without the latter's having become caught, still remained 

 shut at the end of fifteen minutes' observation. 



The force constituting an effective application with a hair is 

 variable, depending on the region of the glochidium stimulated 

 and the physiological state of the individual. At times, a very 

 delicate touch in the more sensitive region calls forth a prompt 

 response; other lots may be practically unresponsive to the gen- 

 tlest touches and require a firmer application. With a fine hair 

 the latter condition is probably more common, although it is, of 

 course, possible that the nearer glochidia approach maturity and 

 the time of natural spawning, the lower the threshold to this sort 

 of stimulation becomes. It was observed in some cases, however, 

 that samples of glochidia, which at one time responded fairly 

 sluggishly and closed slowly, were markedly active a few hours 

 later. 



It follows from the foregoing statements that these experiments 

 are not in accord with the dictum of Lefevre and Curtis that 

 hookless glochidia ''respond either not at all or only sluggishly 

 to tactile stimuh . . . ." The divergence of our conclusions 

 will become more apparent in the pages which follow. 



Having thus established the tactile responsiveness of Lamp- 

 siUs luteola as a type of hookless glochidia, the question of the 

 relation of the hair cells to tactile reception next presents itself. 

 The morphological appearance of these columnar elements 

 suggests the strong probability of a sensory activity of some sort, 

 although actual nervous connections with the muscle fibers have 

 never been demonstrated (p. 466); moreover, their position is 

 such that any relatively large object inserted between the gaping 

 valves will impinge upon them (fig. 4). 



By properly regulating the illumination the outer set of cells 

 can be seen with ease under high binocular magnification. 

 Especially is this true when the valves are viewed rather ob- 

 liquely. The inner sets, on the contrary, cannot be identified 

 with sufficient surety to be of use in experimentation. From 

 stained, permanent preparations it is, however, easy to learn 

 their constant asymmetrical locati on with respect to the adduc- 



