REPRODUCTION IN THE UNIONID^ 
99 
this type made to grasp firmly the point of a needle or the edge of 
a piece of paper by simply touching them between the open valves. 
When once closed in this manner they do not relax but remain 
attached to the object mitil they die. 
Electrical and chemical stimuli may also under proper condi- 
tions bring about permanent closure of the shell. 
The following statement made by Latter (1. c. p. 56) has been 
frequently quoted, especially in text-books, but it has apparently 
never been verified or disproved. ''The Glochidia," he says, 
''are evidently peculiarly sensitive to the odor (?) (sic) of fish. 
The tail of a recently killed Stickleback thrust into a watch-glass 
containing Glochidia throws them all into the wildest agitation 
for a few seconds ; the valves are violently closed and again opened 
with astonishing rapidity for 15-25 seconds, and the animals 
appear exhausted and lie placid with widely gaping shells — unless 
they chance to have closed upon any object in the water (e. g. 
another Glochidium), in which case the valves remain firmly 
closed." Although it is not stated that the tail which caused 
such a commotion among the glochidia had been cut off from the 
fish, it is probable that such was the case. We have repeatedly 
tested glochidia in the same manner both with fins and gills of dif- 
ferent fishes, and, provided that a bleeding surface is not brought 
in contact with the water containing the glochidia, absolutely no 
response on the part of the latter takes place. The result, how- 
ever, is much as Latter describes if a little of the fish's blood gets 
into the water in the neighborhood of the glochidia, except that 
our experience has shown that after snapping for a few seconds 
they come to rest in permanent closure. It, therefore, seems pos- 
sible that the contractions seen by Latter were due to the intro- 
duction of some blood with the tail of the fish, as otherwise agita- 
tion of the glochidia under similar conditions has not been ob- 
served by us. 
Since the hooked and bookless glochidia, whose reactions to 
blood and to certain salts we have examined, behave somewhat 
differently, they are referred to separately below. 
