PARENTAL INSTINCT IN BIRDS. 243 
ereased amount of food-yelk necessary to enable the young birds 
to be hatched in an advanced stage of development, and fully 
equipped to fight the battle of life alone. 
Lichenstein remarks that but for its numerous enemies the 
multiplication of the Ostrich would be quite unequalled, and it is 
a primitive bird with very little parental instinct. 
The fact that the number of eggs varies, ceteris paribus, with 
the risks is well shown by the facts which are known to occur 
among fishes. The Herring (Clupea harengus) lays thousands of 
eges—a fish which possesses no parental instinct, and whose 
egos are exposed to all the dangers and vicissitudes of ocean life. 
The ova of the oviparous Hlasmobranchti are comparatively few in 
number, as they are afforded very considerable protection by a 
tough, leathery, protective envelope. Fishes show a remarkable 
fecundity because they, unlike the birds, do not arrive at a 
permanent size. They grow continuously, and this causes the 
struggle for existence to be severer and the risks greater. 
Birds in these remote times were probably to a great extent 
polygamous, or, at all events, a very loose sort of pairing 
obtained. As there was no need for any parental instinct or 
prolonged care of the eggs, the females and males, after copula- 
tion, had no reason to remain paired off; they had no severe 
mental tax laid upon them such as the care and training of 
young helpless birds entails, and were therefore open to sustain 
the demoralizing effect of promiscuous pairing. Possibly a 
large majority of the fishes are polygamous, and a sort of “‘ pan- 
mixia” appears to occur among amphibians and reptiles of some 
species. 
The Ostrich tribe and a great many of the Galline are poly- 
gamous. The Ostrich (Struthio camelus) presents an interesting 
intermediate stage. She still lays an enormous number of eggs, 
but the male of the species, apparently, has begun to carry out 
the onerous duties of incubation. Though the species is still 
decidedly polygamous,* the females take a share in sitting; the 
male, however, does most of the work.+ If the Ostrich were to 
make any intellectual advance, it would commence with the 
reduction of eggs and wives, and the increase in sexual and 
* On this point cf. 8. C. Cronwright Schreiner, ‘ Zoologist,’ 1897, p. 115. 
D. 
+ Cf. loc, cit., pp. 109-110.—Ep. TD 
