218 
INSTINCT. 
Chap. VII. 
generated. I may add that, according to Dr. Gray 
and to some other observers, the European cuckoo has 
not utterly lost all maternal love and care for her own 
offspring. 
The occasional habit of birds laying their eggs in 
other birds’ nests, either of the same or of a distinct 
species, is not very uncommon with the Gallinacese; 
and this perhaps explains the origin of a singular 
instinct in the allied group of ostriches. For several 
hen ostriches, at least in the case of the American 
species, 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 in 
the case of the cuckoo, at intervals of two or three days. 
This instinct, however, of the American ostrich 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 always lay their eggs in 
the nests of bees of other lands. This case is more re¬ 
markable than that of the cuckoo; for these bees have 
not only their instincts but their structure modified in 
accordance with their parasitic habits; for they do not 
possess the pollen-collecting apparatus which would be 
necessary if they had to store food for their own young. 
Some species, likewise, of Sphegidse (ivasp-like insects) 
are parasitic on other species; and M. Fabre has lately 
shown good reason for believing that although the 
Tachytes nigra generally makes its own burrow and 
stores it with paralysed prey for its own larvae to feed 
on, yet that when this insect finds a burrow already 
made and stored by another sphex, it takes advantage 
of the prize, and becomes for the occasion parasitic. In 
this case, as with the supposed case of the cuckoo, I can 
