164 mr. w. h. hudson on the [Mar. 3, 



— Formerly I believed that though the M. badius is constantly 

 observed to nidificate, they also occasionally dropped their eggs in the 

 nests of other birds (see P. Z. S. 1870, p. 671). I could not doubt 

 that this was the case after having seen a couple of their young fol- 

 lowing a Yellowbreast and being fed by it. But later and more 

 careful observations, together with the discovery I have just recorded, 

 have made me alter my opinion. What then appeared to be proof 

 positive is now uo proof at all ; the young birds I observed were 

 perhaps those of M. rufoaxillaris. Indeed it is much more proba- 

 ble that they should have belonged to this than to the other species, 

 since the Bay-wings are constantly seen to rear their own young, 

 whereas I have never found a nest of M. rufoaxillaris, and believe 

 they are altogether parasitical. 



IX. Reasons for believing that the M. rufoaxillaris is parasitical 

 almost exclusively on M. badius. — I have spoken of the many 

 varieties of eggs M. bonariensis lays. Those of the M. badius 

 are a trifle less in size, in form elliptical, very thickly and uni- 

 formly marked with small spots and blotches of dark reddish 

 colour varying to dusky brown ; the ground-colour is white, but 

 sometimes, though rarely, a very pale blue. It is not- possible to 

 confound the eggs of the two species M. bonariensis and 31. badius. 

 Now, ever since I saw, many years ago, the Yellowbreast already 

 mentioned tending the young Bay-wings, I have looked out for the 

 eggs of the latter species in other birds' nests. I have found many 

 hundreds of uests containing eggs of 31. bonariensis, but never one 

 with an egg of 31. badius, and, I may now add, never with an egg of 

 M. rufoaxillaris. It is wonderful that 31. rufoaxillaris should lay 

 only in the nests of M. badius ; but the most mysterious thing is 

 that 31. bonariensis, which apparently lays in as many nests as 

 ever it can find, never, to my knowledge, drops an egg in the nest of 

 31. badius ! It will be hard for naturalists to believe this ; for if 

 the 31. badius is so excessively vigilant and jealous of all other birds 

 approaching its nest as to succeed in keeping out the subtle, silent, 

 grey-plumaged, ever-present 31. bonariensis, why does it not also 

 keep off the rarer, noisy, bustling, rich-plumaged 31. rufoaxillaris 1 

 But this bird may enter the nest forcibly. The 31. badius may also 

 possess sagacity sufficient to distinguish the eggs of 31. bonariensis 

 from its own and cast them out of the nest. This point must remain 

 unsettled. 



X. Comparative perfection of the parasitical instinct of Molothrus 

 rufoaxillaris. — It is with a considerable degree of repugnance that we 

 regard the parasitical instinct in birds : the reason it excites such a 

 sensation is manifestly because it presents itself to the mind, in the 

 words of a naturalist who lived a hundred years ago and believed the 

 Cuckoo had been created with such a habit, as " a monstrous outrage 

 on the maternal affection, one of the first great dictates of nature" — 

 an outrage, since each creature has been endowed with the all-powerful 

 affection for the preservation of its own, and not another, species ; 

 and here we see it by a subtile process, an uuconscious iniquity, 

 turned from its original purpose, perverted, and made subservient to 



