In systematising from single dead specimens, as to the sex,
age, etc. of which nothing is known, similar errors are unavoidable.
Thus, in order to give another example of very recent date, a celebrated
Ichthyologist, Bleeker, has lately distinguished two groups of the
Cyprinodontes as follows: some, the Cyprinodontini, have a "pinna analis
non elongata," and the others, the Aplocheilini, a "pinna analis
elongata": according to this the female of a little fish which is very
abundant here would belong to the first, and the male to the second
group. Such mistakes, as already stated, are unavoidable by the
"dry-skin" philosopher, and therefore excusable; but they nevertheless
prove in how random a fashion the present systematic zoology frequently
goes on, without principles or sure foundations, and how much it is in
want of the infallible touchstone for the value of the different
characters, which Darwin's theory promises to furnish.) in which the
heart possesses only two pairs of fissures, as it extends forward only
into the second body-segment, and is destitute of the pair of fissures
situated in this segment in other forms.* (* I find, in Milne-Edwards'
'Lecons sur la Physiol. et l'Anat. comp.' 3 page 197, the statement
that, according to Frey and Leuckart, the heart of Caprella linearis
possesses FIVE pairs of fissures. I have examined perfectly transparent
young Caprellae (probably the young of Caprella attenuata, Dana, with
which they occurred), but can only find the usual three pairs.
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