entirely on their
shape, as the images in concave mirrors are very different from
those in convex ones; and so in the same way as the eyes of
animals are of different shapes, and supplied with different
fluids, the ideas of dogs, fishes, men and grasshoppers must be
very different.[5]

[1] _Hyp._. I. 40-61.

[2] _Hyp._. I. 44-46.

[3] _Hyp._. I. 50.

[4] _Hyp._. I. 47.

[5] _Hyp._. I. 49.

In discussing the mental representations of animals of different
grades of intelligence, Sextus shows a very good comprehension
of the philogenetic development of the organs of sense, and
draws the final conclusion that external objects are regarded
differently by animals, according to their difference in
constitution.[1] These differences in the ideas which different
animals have of the same objects are demonstrated by their
different tastes, as the things desired by some are fatal to
others.[2] The practical illustrations given of this result show
a familiarity with natural history, and cognizance of the tastes
and habits of many animals,[3] but were probably few of them
original with Sextus, unless perhaps in their application; that
this train of reasoning was the common property of the Sceptic
School, we know from the fact that Diogenes begins his
exposition of the first Trope in a way similar to that of
Sextus.[4] His illustrations are, however, few and meagre
compared with those of Sextus, and the scientific facts used by
both of them may mostly be found in other authors of antiquity
given in a similar way.[5] The logical result of the reasoning
used to explain the first Trope, is that we cannot compare the
ideas of the animals with each other, nor with our own; nor can
we prove that our ideas are more trustworthy than those of the
animals.[6] As therefore an examination of ideas is impossible,
any decided opinion about their trustworthiness is also
impossible, and this Trope leads to the suspension of judgment
regarding external objects, or to [Greek: epoche.][7]

[1] _Hyp._. I. 54.

[2] _Hyp._. I. 55.

[3] _Hyp._. I. 55-59.

[4] Diog. IX. 11, 79-80.

[5] Pappenheim _Erlauterung Pyrr. Grundzuege Par_. 41.

[6] _Hyp_. I. 59.

[7] _Hyp_. I. 61.

After reaching this conclusion, Sextus introduces a long chapter
to prove that animals can reason. There is no reference to this
in Diogenes, but there is other testimony to show that it was a
favourite line of argume