GLOCHIDIA — FACTORS UNDERLYING ENCYSTMENT 475 



others shut almost completely and then open immediately. It is 

 interesting to find that glochidia in such an apparently irritable 

 condition do not have a noticeably augmented sensitivity to 

 ordinary tactile stimulation. 



It may be thought that since a hair, relatively small and hard, 

 is not the sort of substance to which glochidia are destined to 

 attach, other softer and larger objects might elicit still more ready 

 responses. (Yet it is well to remark at this point that a thread 

 or cord separated into its component strands to form a brush, 

 and dragged through a suspension of glochidia for a short time, 

 becomes clasped by many larvae fp. 488j.j However, it is true 

 that a softer, larger object that fits better between the valves 

 produces superior results. Such a satisfactory agent is found in 

 a tiny shaving of cork, cut by a razor to a sword shape, like a gill 

 filament. Glochidia attach readily to the point or edges of this 

 flexible object. The best responses are naturally obtained with 

 a gill filament itself, the soft, lamellated tissue demonstrably 

 conforming to the space between the valves. The increased 

 responsiveness by this sort of treatment is probably dependent 

 upon the stimulation of more sense organs, which, in its last 

 analysis, is a question of surface area of contact. The theoretical 

 possibility of a chemical influence from a gill will be considered 

 later (p. 488) ; it need not concern us here. 



b. Lampsilis ligamentina responds actively to stimulation with 

 a hair, but probably not quite as sharply as L. luteola. These 

 glochidia also attach to yarn unraveled into a brush and agitated 

 with them. They likewise attach very readily to fine cork 

 shavings. 



c. Lampsilis anodontoides gave results very similar to L. 

 ligamentina. 



d. Lampsilis gracilis glochidia, although very small, respond 

 rather promptly to stimulation with a hair. They are so small 

 it is difficult to localize the stimulus accurately. 



2. Axe-head glochidia. The species available was Proptera 

 (Lampsilis) laevissima ffigs. 5 and 6). The valves are extremely 

 short in anteroposterior extent, and are capable of opening very 

 wide; in this position they present an elongate oblong shape. 



