206 Henry LEsLIE OsBorn, 
preference for Anodonta, and if, for any reason, the numbers of 
Cotylaspis in the lake are limited to the number that can be accom- 
modated by the Anodonta population, then we should not expect to 
find them outside of that form. The idea of a comparatively recent 
arrival of the flukes in Lake Chautauqua would harmonize with this 
interpretation of the distribution. Kenzey’s list of localities includes, 
besides the Schuylkill system and the Mississippi system, the Susque- 
hanna River system as included in the distribution of Cotylaspis. It 
will be interesting to find whether it occurs in other rivers of this 
country. It appears probable that it is much more common in this 
country than in other parts of the world. 
A summary of these facts includes the following points: 
Cotylaspis is confined to Anodonta and not found in Umio. 
It is nearly universally present in Anodonta. 
Its numbers are not in direct relation with the size and age 
of Anodonta. 
Its numbers vary directly with the purity or impurity of the 
water in which the host is found. 
c) Habits. 
C. insignis is most commonly found (Fig. 1) adhering very firmly 
by its huge ventral sucker to the cloacal surface of the kidney of 
its host. It is occasionally found on the adjacent margin of the 
inner gill or of the visceral mass. In the living animal the anterior 
part of the body “neck” is kept incessantly swaying from side to 
side, and attaching by the oral end. Under a simple microscope a 
series of events can be seen to occur as follows: the neck is stretched 
out, the tip is dilated greatly into a very thin flat disk (Fig. 2) 
and applied to the kidney surface, where sometimes it adheres 
strongly for a time but more commonly it is drawn together by the 
contraction of the rim, thus sweeping across the skin of the host and 
gathering up materials which may have collected there. The neck 
is next contracted very much (/ in Fig. 4) at the same time the 
sweeping is swallowed, movements for the purpose being seen in 
the pharynx. The neck is again thrust forward and the same move- 
ments repeated generally on the opposite side. The fluke does not 
change its base from time to time, as one would expect. To test 
this, which I had begun to suspect, I pinned an Anodon open under 
water at 9.30 A. M. and noted the exact position of two flukes. 
Twenty-four hours later they had not moved from the original 
