100 GEORGE LEFEVRE AND WINTERTON C. CURTIS 
Reactions of hookless glochidia 
The glochidia of Unio complanatus were used in the following 
experiments. When a small drop of blood of either the killifish, 
Fundulus diaphanus, or the white perch, Morone americana, was 
placed over the glochidia contained in a small amount of water 
in a watch-glass, the effect was immediate and very striking. 
Every glochidium was thrown into rapid and violent contrac- 
tions, alternating with relaxations, the edges of the valves either 
quite or nearly touching with each snap. Where the stimulus 
was strongest, that is, immediately under the drop of blood, the 
glochidia exhibited two or three strong contractions and then re- 
mained closed, but proceeding outwards to zones of diminishing 
intensity, the snapping occurred intermittently for from ten to 
fifty seconds. Here the contractions were quite rapid at first, 
one or two every second, but soon the intervals became longer, 
until finally the activity was ended by the closure of the valves. 
In some cases it was observed that after the first few snaps the 
muscle did not completely relax and each subsequent contraction 
caused the valves to describe a shorter arc. 
Since the hookless glochidia are essentially gill parasites and, 
when taken into the mouth of the fish, lodge among the gill-fila- 
ments, abrasions of the delicate epithelium covering the latter 
always occur and produce more or less extensive hemorrhage from 
the blood capillaries. It is, therefore, evident that blood exud- 
ing in the neighborhood of the glochidia must have the same 
effect as in our experiments, and, by causing vigorous contrac- 
tions of the adductor muscle, be eflicacious in bringing about a 
firm and permanent attachment to the filaments. And, further- 
more, since glochidia of the hookless type only occasionally ex- 
hibit spontaneous contractions, and, unlike the hooked forms, 
respond either not at all or only quite sluggishly to tactile stimuli, 
the action of the blood upon them must play an important part 
in securing their attachment to the gills. 
A series of experiments was also undertaken for the purpose 
of determining the reactions of the glochidia of Unio complanatus 
to solutions of several different salts, a brief account of which 
