REASON. 
117 
appropriate breeding-places for these birds. The spring 
of 1865 made its appearance very suddenly, the winter 
holding on with exceptional severity up to almost the last 
moment; the interim between icy coldness and warm 
spring weather scarcely lasted a fortnight. I foretold the 
change, though neither the thermometer nor the baro¬ 
meter gave me reason to expect it, but the aquatic birds of 
the Hamburg Zoological Gardens did. They had passed 
the whole of this severe winter out of doors, and for this 
reason were getting rather mopy towards the end of the 
time. All of a sudden this behaviour changed; they 
paired off, and courtship began, in spite of ten degrees of 
cold; I then knew that spring would soon arrive: sure 
enough it came, and when the first eggs were laid, ice 
and snow had vanished. 
It is difficult to give an explanation of these facts ; 
that they should be the effect of chance is impossible ; 
the great number of individual cases goes to disprove 
such an explanation. The length of time between the 
changes is a sufficient negation of the idea that it is 
possible to attribute them to an extraordinary sensibility 
of atmospheric influence. Assuming that presentiment 
in a bird is purely an internal sensation of which it 
becomes conscious, it must seem incomprehensible to us 
how it can make arrangements months beforehand in 
anticipation of the dreaded change, for we can have no 
idea of so delicate a nervous organization in an animal. 
The mechanical knowledge of some animals, which is 
also ascribed by many to instinct, appears to me easier 
to be understood than their knowledge of the weather. 
We speak of the mechanical instinct of insects gene¬ 
rally with more astonishment than admiration, although 
the latter is not entirely wanting, and one raises this 
R 
