indispensable for arrival at a just conclusion could not have been
thus acquired. This may be done as follows: {111} for, Firstly, the
facts in question lie in the future, and the present gives no ground
for conjecturing the time and manner of their subsequent development.

Secondly, they are manifestly debarred from the category of
perceptions perceived through the senses, inasmuch as no information
can be derived concerning them except through experience of similar
occurrences in time past, and such experience is plainly out of the
question.

It would not affect the argument if, as I think likely, it were to
turn out, with the advance of our physiological knowledge, that all
the examples of the first case that I am about to adduce reduce
themselves to examples of the second, as must be admitted to have
already happened in respect of many that I have adduced hitherto.
For it is hardly more difficult to conceive of a priori knowledge,
disconnected from any impression made upon the senses, than of
knowledge which, it is true, does at the present day manifest itself
upon the occasion of certain general perceptions, but which can only
be supposed to be connected with these by means of such a chain of
inferences and judiciously applied knowledge as cannot be believed to
exist when we have regard to the capacity and organisation of the
animal we may be considering.

An example of the first case is supplied by the larva of the stag-
beetle in its endeavour to make itself a convenient hole in which to
become a chrysalis. The female larva digs a hole exactly her own
size, but the male makes one as long again as himself, so as to allow
for the growth of his horns, which will be about the same length as