ORTMANN: THE CRAWFISHES OF THE STATE OF PENNSYLVANIA 497 
actually eat and damage crops to a considerable degree. As I have observed, in 
captivity C. monongalensis and C. diogenes eat young plants, and they surely do so 
when not in captivity, young sprouting corn, buckwheat, ete., being rather succulent 
and attractive to them. If sown ina place where crawfishes abound these crops will 
surely be attacked. 
This being the case, and besides the chimneys being also a nuisance, it might 
be desirable to exterminate the crawfishes in a given locality, or at any rate to 
reduce their numbers. For this purpose unslacked lime, the means employed by 
the farmers at Selbysport, might be used. But I am in no position to vouch for 
the efficiency of this remedy, having no personal experience (with the exception of 
the one case mentioned aboye, p. 346). I simply report what was told me. 
Another way might be to drain the places where crawfishes are plentiful. But 
this hardly will be as efficient a means as desired. Drainage only lowers the level 
of the groundwater, and in the case of C. carolinus, which is the chief offender, we 
know that it digs down sometimes over three feet to reach the groundwater. In 
Rainier Park at Ohiopyle this species used to be very abundant, but the draining 
of the park has reduced its numbers. Still it is present there, and the chimneys 
are thrown up all over the lawn, where the holes must in places go down at least 
three feet before reaching water. Thus, although a decrease in numbers may be 
brought about by drainage, a complete extermination by this method must not be 
expected. 
Another form of damage done by chimney-builders is known. They are reported 
to burrow into and to do damage to the dams on ponds, reservoirs, and rivers. 
(The levees of the Mississippi. See Ortmann, 1900, p. 1262.) No instances of this 
kind are known to me in Pennsylvania. In one case, at the reservoir of McGee 
Run, at Derry, Westmoreland County, I saw holes of C. diogenes not only along the 
banks, but also in the dam. ‘The specimens were all young, and the holes small, 
since this reservoir has existed only for a few years. But it would not be astonish- 
ing if the crawfishes should gradually work deeper into the dam, finally causing 
serious damage. 
Vil. BEARING OF THE ABOVE STUDIES ON THE THEORY OF 
EVOLUTION. 
Our observations on the Pennsylvania crawfishes, morphological, ecological, and 
geographical, serve to illustrate certain phases of the process of evolution, and certain 
theories propounded in connection with them. Naturally they do not elucidate 
this process in its fullest scope. Thus I shall only pick out a few points upon which 
my observations may have some bearing. 
