not the case in the familiar parasitic unions where one 

 animal, usually a lower one, lives on or within a higher 

 one, and largely at its expense. The association may 

 be a temporary attachment, or a life-long union, as 

 intimate as that of different organs of the same animal. 

 But it is never a profitable partnership; it is not co- 

 operative living, or mutually serviceable; the net con- 

 structive result is always something lost, never some- 

 thing gained. 



Parasites, as a rule, are of good antecedents; the 

 degenerate descendents of animals which once possessed 

 the means of living free and independent lives. As para- 

 sites they live at the expense of some more active and 

 more highly organized animal than themselves; im- 

 mersed, it may be, in the food its host has captured and 

 digested for its own use, and dependent for transpor- 

 tation and protection on its host's superior freedom of 

 movement, and its superior power to fight the battles 

 of life. 



The only important functions to be performed by 

 such an animal as a tapeworm, for example, are to 

 make sure of its own position in life, and by not com- 

 pletely destroying its host, to insure a similar sinecure 

 for its descendants. 



The methods by which such highly specialized 

 parasites maintained their position in life are exceed- 

 ingly intricate and cunning devices, more elaborate in 

 some respects than those utilized by their more highly 

 organized hosts. But nothing is really gained thereby, 

 for the methods are not broadly constructive. They 

 are based on the robbers' doctrine, and the gamblers', 

 of how best to gain something for nothing. But the 

 successful parasite, after all, does pay too large a price 



