1874.] MOLOTHRI OF BUENOS AYRES. 165 



the very opposing agency against which it was intended as a safe- 

 guard ! The formation of such an instinct seems indeed like an un- 

 forseen contingency in the system of nature, a malady strengthened, 

 if not induced, by the very laws established for the preservation of 

 health, and which the vis medicatrix of nature is incapable of elimi- 

 nating. 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 stu- 

 pidity. In the competition for place, the struggle for existence, 

 said with reason to be most deadly between such species as are most 

 nearly allied, the operations are imperceptible, the changes so gra- 

 dual," 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 saga- 

 city to escape its persecutions ; so that the war is not one of extermi- 

 nation, 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 cau, c e its degeneration. But we can conceive no 

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

 thrus, destructive to such myriads of lives in their beginning. And 

 inasmuch 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 1 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 advan- 

 tage. 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, however we view the parasitical habit, it 

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

 should we attempt to mentally create a perfect parasitical instinct 

 (that is, one that would be thoroughly efficient with the least pos- 

 sible prejudice for or injustice towards another species ; for the pre- 

 servation of the species on which the parasite is dependant is neces- 



