212 SPECIAL IXSTLNOTS. Ciiai-. VII. 



which caiiiioL be disputed — then the instincts and structure of 

 the youns-;' could be slowly modified as well as those of the 

 adult; antl both cases must stand or fidl with the whole theory 

 of natural selection. 



The occasional habit of birds laying their eggs in other 

 birds' nests, either of the same or of distinct species, is not 

 very uncommon with the Gallinaceas ; and this perhaps explains 

 the origin of a singular instinct in the nearest allied group, 

 that of ostriches. For several hen-ostriches unite and lay first 

 a few eggs in one nest and then in another; and these arc 

 hatched by the males. This instinct may probably be accounted 

 for by the ftict of the hens lajang a large number of eggs, but, 

 as in the case of the cuckoo, at intervals of two or three days. 

 The 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. 



T\Iany 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 Avould have been indispensable if they had 

 stored food for tlieir own yoimg. Some species, likewise, of 

 Sphegida) (wasp-like insects) are parasitic in the same manner 

 on other species ; and M. Fabre has lately shown good reason 

 for believing that, although the Tachytes nigra generally makes 

 its OAvn burrow and stores it with paralyzed prey for its own 

 larv;e, 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 Avith 

 the supposed case of the cuckoo, I can see no difficulty in nat- 

 ural selection making an occasional habit permanent, if of ad- 

 vantage to the species, and if the insect, whose nest and stored 

 food are thus feloniously appropriated, be not thus extermi- 

 nated. 



Slave-male hip Instinct. — This remarkable instinct Avas first 

 discovered in the Formica (Polyerges) rufesccns by Pien-o 

 Huber, a better oliserv-er even than his celebrated father. This 

 ant is absolutely dependent on its slaves ; Avithout their aid, 

 the species Avould certainly become extinct in a single year. 

 The males and fertile females do no Avork of any kind, and the 

 Avorkers or sterile females, though most energetic and coura- 



