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Show 194 INSTINCT. [Cn.AP. VII. occasionally she laid an egg in another bird's nest. If the old bird profited by this occasional habit, or if the young were made more vigorous by advantage having been taken of the mistaken maternal instinct of another bird, than by their own mother's care, encumbered as she can hardly fail to be by having eggs and young of different ages at the san1e tin1e ; then the old birds or the fostered young would gain an advantage. And analogy would lead me to believe, that the young thus reared would be apt to follow by inheritance the occasional and aberrant habit of their mother, and in their turn would be apt to lay their eggs in other birds' nests, and thus be successful in rearing their young. By a continued process of this nature, I believe that the strange instinct of our cuckoo could be, and has been, generated ... I may add that, according to Dr. Gray and to some other observers, the European cuckoo has not utterly lost all 1naternal 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 Gallinaceoo ; 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 .A1nerican speci'es, 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 kinds. This case is more remarkable 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 h~d to store food for their own young. Some CH.AP. VII.] SLAVE-MAKING INSTINCT. 195 species, likewise, of Sphegidoo (wasp-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 larvoo 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 see no difficulty in natural selection making an occasional habit permanent, if of advantage to the t:pecies, and if the insect whose nest and stored food are thus feloniously appropriated, be not thus exterminated. Slave-making instinct.-This remarkable instinct was fi~st discovered in the Formica· (Polyerges) rufescens by Pierre I-Iuber, a better observer even than his celebrated father. This ant is absolutely dependent on its slaves ; wit~out. their. aid, the species ·would certainly become extrnct In a single year. The males and fertile females do no work. The workers or sterile females, though most energetic and courageous in capturing slaves, do no other work. They are incapable of making their own nests, or of feeding their own larvoo. When the old nest is found inconvenient, and they have to migrate, it is the slaves which determine the migration, and actually carry their masters in their jaws. So utterly helpless are the Inasters, that when I-Iuber shut up thirty of thmn without a slave, but with plenty of the food which they like best, and with their larvoo and pupoo to stimulate them to work, they did nothing ; they could not even feed themselves, and many perished of hunger. I-Iuber then introduced a single slave (F. fusca), and she instantly set to work, fed and saved the survivors ; made s01ne cells and tended the larvoo, and put all to rights. What can be more extraordinary th~n these well-ascertained facts? If we had not known of any other slave-making ant, it would have been hopeless to have speculated how so wonderful an instinct could have been perfected. Formica sanguinea was likewise discovered by P. Huber to be a slave-making ant. This species is found in |