it to obtain its needed nourishment. On the contrary, good
observers state that many young pigs, puppies, and kittens
would fail to find the teat altogether unless helped by
the mother, while of the lamb Mr. Hudson says:--

"It does not know what to suck. It will take into its mouth
whatever comes near, in most cases a tuft of wool on its dam's
neck, and at this it will continue sucking for an indefinite time."

It is, he thinks, the strong smelling secretion of the udder
that at length attracts the lamb. ¹

Heredity is the main guide in the matter and manner
of eating and drinking, but the young bird, however much
in need of drink, gives no response to the presence or
even to the touch of water till it has once got it inside
its bill by a more or less accidental peck. ²

There is no more wonderful operation of "instinct"
than the nest of the bird, or the web of the spider. But
neither of these is in all cases immutable in type nor perfect
from birth. Dahl ³ found with one species of spider, which
makes a web with one section omitted and the space
occupied by a single thread, that the first web spun is of a
more primitive type. It is made complete, like an ordinary
web. The more developed form is found sometimes in
the second web, sometimes after several repetitions. One
individual combined the single thread with the perfect web.
The nest-building of birds is unquestionably instinctive, but
as unquestionably it is an art which different individuals
of the same species possess in different degrees of perfec-
tion, ⁴ and which is modifiable in many different ways, as
circumstances suggest or require. ⁵

Few instincts seem more mysterious than those which
lead insects to choose for depositing their eggs precisely
those places which are best adapted for hatching out the
larva. Yet the flesh fly has been known to deposit its

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