102 
G EORGE LEFEYEE AND WINTER TON C. CURTIS 
occurs is quite different from that sho^vn b}^ the glochidia of 
Unio complanatus under similar conditions. Instead of being 
thrown into violent and rapid snapping, the valves closing and 
opening alternately, there is only partial recovery after each con- 
traction, while the valves are brought closer and closer together 
by a series of short jerks. The final act of closing is interesting. 
As soon as the points of the hooks touch, the contraction of the 
adductor muscle becomes continuous and the hooks are slowl}^ 
bent inwards against each other. Under the steady pressure ex- 
erted by the muscle, aided probably by the action of the myocytes, 
which have been described by Schmidt ('85 h), the spines on the 
outer surface are apposed and the hooks turned in completeh^ 
between the valves, the margins of which are brought together, 
if no object intervenes. It will be readily understood that, owing 
to the turning in of the hooks, the spines are pressed into the fish's 
tissues, when attachment to the host takes place, and a firm hold 
is thereby secured. 
When the glochidia of Symphynota complanata were exposed 
to salt solutions, the contractions produced were of the kind just 
described. KCl, KNO3, and NH4CI in solutions of 0.5 to 1.0 
per cent caused a few successive jerks, the contractions being more 
vigorous and closure occurring sooner with the stronger solutions. 
NaCl and Na2C204 in the same strength acted less energetically, 
and it was necessary to use a two per cent solution to produce the 
same effect as was obtained with the weaker solutions of potassium 
and ammonium salts. A 0.5 per cent solution of CaCl2 produced 
no contractions, while a 1.0 per cent solution after a latent period 
of fifteen minutes caused either partial or complete closure of 
the valves. MgCl2 and MgS04, in solutions of 0.5 and 1.0 per 
cent, inhibited contractions, and when the glochidia were allowed 
to remain in them they finally died in the expanded condition. 
When the Mg salts, however, were used in stronger solutions 
closure of the valves occurred after a few spasmodic contractions. 
