68 MIND IN EVOLUTION CHAP. 



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 



1 Lloyd Morgan, Habit and Instinct, pp. 114-116. Cf. Preyer, I. 

 pp. 138-140, and Wesley Mills, pp. 118, 119. 



2 See Craig, Observations on Doves Learning to Drink, J. A. B. 1912, 

 pp. 273-279, and Lloyd Morgan, Habit and Instinct, pp. 44-46, there 

 cited. 3 Dahl, p. 168. 



4 See Lloyd Morgan, Habit and Instinct, p. 234 et seq. 

 6 For abundant evidence, see Romanes, M.E.A. p. 209 ff. and Wallace, 

 Natural Selection, p. no et seq. 



