REPRODUCTIOX IN THE UNIONID^ 
103 
THE PARASITISM 
The only infections which we have ever observed in nature were 
of Anodonta grandis, found in the month of November, infect- 
ing the roach (Abramis crysoleucas), German carp (Cyprinus car- 
pio), yellow perch (Perca flavescens,) blue-gill sunfish (Lepomis 
pallidus), rock bass (Ampbloplites rupestris) and crappie (Pomoxis 
annularis), collected from the Mississippi River at LaCrosse, Wis- 
consin. At that time, we handled over 25,000 fish and from the 
finding of these glochidia upon a majority of the fish taken at 
random for examination in connection with our own infections 
it seemed that a large proportion of the whole number were lightly 
infected with this glochidium. By actual count, we found from 
one to twenty upon a fish and they were all in about the stage 
shown by fig. 23. These fish had been recently collected from 
sloughs, similar to those in which we found many individuals of 
A. grandis with ripe glochidia, and this probably represented a 
typical infection under natural conditions, where we may be sure 
that maximum infections never obtain. 
Following the methods of artificial infection as practiced since 
the work of Braun ('78) and Schmidt C85), we have obtained un- 
limited material by confining the fish in small receptacles to which 
the glochidia have been added by washing from the gills of the 
clams. It is only necessary to see that the glochidia are so dis- 
tributed in the water as to come in contact with the proper part 
of the fish, and in most cases, to guard against over, rather than 
under, infection. Active fish, such as the rock and the large- 
mouthed black bass, are very favorable for gill infections, since 
they keep the water so well agitated that the glochidia hardly 
settle to the bottom at all, while their strong respiratory move- 
ments draw the suspended glochidia continually against the gills. 
Fish like the crappie, which when undisturbed move about quietly 
and whose respiratory movements are less vigorous, must have 
the water stirred to keep the glochidia suspended, or so shallow 
that the fish are always near the bottom. The smaller gill slit 
of the crappie is another factor which makes for a very light in- 
fection in fish under two inches in length, since the glochidia 
