PROCEEDINGS 



OF THE 



Delaware County Institute of Science 



Vol. VI, No. 3 April, 191 i 



PARASITIC ADAPTATION. NEW yo 



*iOTANlC 



BY B. M. UNDERHILL, V. M. D. _,^ 



U4JU)Q 



Living things upon cursory observation appear to be at 

 peace with one another, and little may be noticed that is dis- 

 turbing to the harmony between the organism and its environ- 

 ment. We find, however, on more careful examination, that 

 there are sources of constant interference operating to destroy 

 organisms, to restrict their multiplication, or even bring about 

 their total extinction. Animals prey one upon another, and 

 drive each other from a favorable to an unfavorable habitat, 

 while changes in the earth's surface and in climatic condi- 

 tions make localities inhospitable to certain animal groups 

 which previously had thrived amid favorable surroundings. 

 There is, in fact, a perpetual " struggle for existence " which 

 may lead to the seeking of shelter from the conflict in a 

 changed and often degenerate mode of life to which the 

 animal becomes adaptively modified. Thus, through such 

 influences, we may have a terrestrial animal driven to an 

 arboreal or even an aquatic or semi-aquatic existence. A 

 defenseless little member of the Insectivora burrows and 

 becomes subterranean, while another finds protection in the 

 nocturnal habit, others seek the shelter of caves or rock crev- 

 ices, and we often find creatures, usually somewhat degene- 

 rate, in places which seem to us quite unfavorable to the sup- 

 port of even the higher invertebrates. While in such cases 



