862 THE ORIGIN OF SPECIES 



They either build a nest of their own, or seize on one 

 belonging to some other bird, occasionally throwing out 

 the nestlings of the stranger. They either lay their eggs 

 in the nest thus appropriated, or oddly enough build one 

 for themselves on the top of it. They usually sit on 

 their own eggs and rear their own young; but Mr. Hud- 

 son says it is probable that they are occasionally para- 

 sitic, for he has seen the young of this species following 

 old birds of a distinct kind and clamoring to be fed by 

 them. The parasitic habits of another species of Molo- 

 thrus, the M. bonariensis, are much more highly devel- 

 oped than those of the last, but are still far from perfect. 

 This bird, as far as it is known, invariably lays its eggs 

 in the nests of strangers; but it is remarkable that sev- 

 eral together sometimes commence to build an irregular 

 untidy nest of their own, placed in singularly ill-adapted 

 situations, as on the leaves of a large thistle. They 

 never, however, as far as Mr. Hudson has ascertained, 

 complete a nest for themselves. They often lay so many 

 eggs — from fifteen to twenty — in the same foster-nest that 

 few or none can possibly be hatclied. They have, more- 

 over, the extraordinary habit of pecking holes in the 

 eggs, whether of their own species or of their foster- 

 parents, which they find in the appropriated nests. They 

 drop also many eggs on the bare ground, which are thus 

 wasted. A third species, the M. pecoris of North Amer- 

 ica, has acquired instincts as perfect as those of the 

 cuckoo, for it never lays more than one egg in a 

 foster-nest, so that the young bird is securely reared. 

 Mr. Hudson is a strong disbeliever in evolution, but he 

 appears to have been so much struck by the imperfect 

 instincts of the Molothrus bonariensis that he quotes my 



