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. monoiiijalensis and C. diogenes eat young plants, and they surely do so 

 when not in captivity, young sprouting corn, buckwheat, etc., being rather succulent 

 and attractive to them. If sown in a place where crawfishes abound these crops will 

 surely be attacked. 



Tliis being the case, and besides the chimney's being also a nuisance, it might 

 be desirable to e.Kterminate the crawfishes in a given locality, or at any rate to 

 reduce their numbers. For tliis purpose unslacked lime, the means employed by 

 the farmers at Selbysport, might be used. But I am in no position to vouch for 

 the eflficiency of this remedy, having no personal experience (with the exception of 

 the one case mentioned above, p. 346). I simply report what was told me. 



Another way might bo 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 gi'ound water. In 

 Rainier Park at Ohiopyle this species used to be very al)undant, but the draining 

 of the park has reduced its numbers. Still it is present there, and the chimneys 

 are thrown up all owr 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-buildei*s is known. They are reported 

 to burrow into and to do damage to the dams on ponds, reservoii-s. 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 Mc( iee 

 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 onl}' for a few years. But it would not be astonish- 

 ing if the crawfishes should gradually work deeper into the tlam, finally causing 

 serious damage. 



VII. JU:.\RlN<i OF THE ABOVE STUDIES UN lllK TllEoUV V\' 



EX'OLUTION. 

 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. 



