622 REPORT OF NATIONAL MUSEUM, 1893. 



that tbe (liiniuution and final disappearance of one species is never 

 attributed to a corresponding increase in another more favored species 

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

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

 liad ([uietly entered on the possession of an inheritance that was theirs 

 by riglit. Mighty as are tlie results worked out by such a process, it 

 is only by a somewhat strained metaphor that it can be called a strug 

 gle. But even when tlie 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 degeueration. 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 

 inasmuch as their preservation is inimical to the species ou which they 

 are i)arasitical, there must also here be a struggle. But what kind of 

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

 that gives greater streugth to the victor, but an anomalous struggle in 

 which one of tlie combatants has nuide his adversary turn his weajjons 

 against himself, and so seems to have an infinite advantage. It is 

 impossible for him to suffer defeat; and yet, to follow out the meta- 

 phor, he has so wormed about and interlaced liimself with his oppo- 

 nent that as soon as he succeeds iu 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 j 

 consequently the struggle, nnequal as it appears, must continue for- 

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

 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 thoronghly efficient with the least possible prejudice to 

 or injustice toward another species — for tlie ])reservation of the spe- 

 cies on which the parasite is dependent is necessary to its own) by 

 combining in imagination all known parasitical habits, eliminating 

 every ofi'ensive quality or circumstance, and attributing such others 

 in their place as we should think fit, our conception would probably 

 still fall short in simplicity, beauty, and completeness of the actual 

 instinct of M. rufoaxillaris. Instead of laying its eggs promiscuously 

 in every receptacle that offers, it selects the nest of a single species; so 

 that its selective instinct is related to the adaptive resemblance in its 

 eggs and young to those of the species ou which it is parasitical. Such 

 an adaptive resemblance could not, of course, exist if it laid its eggs 

 in the nests of more than one species, and it is certainly a circumstance 

 eminently favorable to preservation. Then, there not being any such 



