AMERICAN MIDLAND NATURALIST. 177 
a movement among mammals. Something similar is going on 
among the insects. In each of these classes it is undoubtedly 
the result of deforestation, but if there is a similar movement 
of the fishes, it is far more difficult to explain. 
comparison of percentage given above for the two per- 
iods seems to indicate that small species have a slight advan- 
tage, and that species numerous in the region are more apt 
to survive than those that are rare, without regard to their 
abundance in any particular stream. No tendency with re- 
gard to food is evident. It is of interest to note that but two 
of the seven cat fishes occurring at the earlier period were 
found at the later date, while only one of the eight darters 
had disappeared. 
e data are insufficient to warrant any sweeping con- 
clusions but a reduction in the number of species has taken 
place without question and it is, perhaps, the most significant 
fact to be learned from this study. i 
MOLLUSCA AND CRUSTACEA. 
s 
entrance of their burrows and these “craw-fish chimneys” are 
conspicuous features of many poorly drained pastures and 
meadows. As land has become more valuable, these swampy 
places have been tiled or ditched and often placed under culti- 
vation. Consequently they have become unfit for crustacean 
inhabitants and the latter must have diminished. 
In the ponds, lakes and streams, the same conditions that 
affect the fish fauna(p. 174.) have acted upon the aquatic Crus. 
tacea and Mollusca. Deforestation has brought floods that 
have torn up stream bottoms in the course of an hour. Si 
, 
e 
