INSTINCT 363 



words, and asks, *'Must -we consider these habits, not 

 as especially endowed or created instincts, but as small 

 consequences of one general law, namely, transition?" 



Various birds, as has already been remarked, occa- 

 sionally 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 Ameri- 

 can 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 in- 

 sects) are likewise parasitic; and M. Fabre has lately 

 shown good reason for believing that, although the 

 Vachytes nigra generally makes its own burrow and 

 stores it with paralyzed prey for its own larvae, yet 

 that, when this insect finds a burrow already made and 

 stored by another sphex, it takes advantage of the prize, 



