CHAP. VIII.] INSTINCTS OF THE MOLOTHRUS. 201 



says it is probable that they are occasionally parasitic, for he has 

 seen the young of this species following old birds of a distinct 

 kind and clamouring to be fed by them. The parasitic habits of 

 another species of Molothrua., the M. bonariensis, are much more 

 highly developed 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 several 

 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 hatched. They have, 

 moreover, 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 America, 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 words, and asks, "Must 

 we consider these kabits, not as especially endowed or created 

 instincts, but as small consequences of one general law, namely, 

 transition 1 " 



Various birds, as has already been remarked, occasionally lay 

 their eggs in the nests of other birds. This habit is not very 

 uncommon with the Gallinaceae, and throws some light on the 

 singular instinct of the ostrich. In this family several hen-birds 

 unite and lay first a few eggs in one nest and then in another; and 

 these are hatched by the males. This instinct may probably be 

 accounted for by the fact of the hens laying a large number of 

 eggs, but, as with the cuckoo, at intervals of two or three days. 

 The instinct, however, of the American ostrich, as in the case of 

 the Molothrus bonariensis, has not as yet been perfected ; for a 

 surprising number of eggs lie strewed over the plains, so that in 

 one day's hunting I picked up no less than twenty lost and 

 wasted eggs. 



Many bees are parasitic, and regularly lay their eggs in the 

 nests of other kinds of bees. This case is more remarkable than 

 that of the cuckoo ; for these bees have not only had their instincts 

 but their structure modified in accordance with their parasitic 

 habits; for they do not possess the pollen-collecting apparatus 

 which would have been indispensable if they had stored up food 

 for their own young. Some species of Sphegidse (wasp-like 



