94 ICTERID^E. 



induced, by the very laws established for the preservation of health, 

 and which the vis medicatrix of nature is incapable of eliminating. 

 Again, the egg of a parasitical species is generally so much larger, 

 differing also in coloration from the eggs it is placed with, whilst 

 there is such an unvarying dissimilarity between the young bird 

 and its living or murdered foster-brothers, that, unreasoning as we 

 know instinct, and especially the maternal instinct, is, we are shocked 

 at so glaring and flagrant an instance of its blind stupidity. 



In the competition for place, the struggle for its existence, said with 

 reason to be most deadly between such species as are most nearly allied, 

 the operations are imperceptible, and the changes are so gradual, that the 

 diminution and final disappearance of one species is never attributed 

 to a corresponding increase in another more favoured species over 

 the same region. It is not as if the regnant species had invaded 

 and seized on the province of another, but appears rather as if they 

 had quietly entered on the possession of an inheritance that was theirs 

 by right. Mighty as are the results worked out by such a process, it is 

 only by a somewhat strained metaphor that it can be called a struggle. 

 But even when the war is open and declared, as between a raptorial 

 species and its victims, the former is manifestly driven by necessity. 

 And in this case the species preyed on are endowed with peculiar sagacity 

 to escape its persecutions ; so that the war is not one of extermination, 

 but, as in a border war, the invader is satisfied with carrying off the 

 weak and unwary stragglers. Thus the open, declared enmity is 

 in reality beneficial to a species; for it is sure to cut off all such 

 individuals as might cause its degeneration. But we can conceive no 

 necessity for such a fatal instinct as that of the Cuckoo and Cow-bird 

 destructive to such myriads of lives in their beginning. And inas- 

 much as their preservation is inimical to the species on which they 

 are parasitical, there must also here be a struggle. But what kind 

 of struggle? Not as in other species, where one perishes in the 

 combat that gives greater strength to the victor, but an anomalous 

 struggle in which one of the combatants has made his adversary turn 

 his weapons against himself, and so seems to have an infinite advantage. 

 It is impossible for him to suffer defeat ; and yet, to follow out the 

 metaphor, he has so wormed about and interlaced himself with his 

 opponent that as soon as he succeeds in overcoming him he also must 

 inevitably perish. Such a result is perhaps impossible, as there are 

 so many causes operating to check the undue increase of any one 

 species : consequently the struggle, unequal as it appears, must con- 

 tinue for ever. Thus, in whatever way we view the parasitical habit, it 

 appears cruel, treacherous, and vicious in the highest degree. But 



