Facts and Arguments for Darwin | Page 4

same
importance in Darwin's favour, that his opponents have attributed to the
absence of demonstrated intermediate forms between the species of the
various strata of the earth. Independently of the reasons which Darwin
gives for the preservation of such intermediate forms being only
exceptional, this last mentioned circumstance will not be regarded as of
very great significance by any one who has traced the development of
an animal upon larvae fished from the sea, and had to seek in vain for
months, and even years, for those transitional forms, which he
nevertheless knew to be swarming around him in thousands.
A few examples may show how contradictions might come forth as
necessary results of the Darwinian hypotheses.
It seems to be a necessity for all crabs which remain for a long time out
of the water (but why is of no consequence to us here), that air shall
penetrate from behind into the branchial cavity. Now these crabs,
which have become more or less estranged from the water, belong to
the most different families--the Raninidae (Ranina), Eriphinae (Eriphia
gonagra), Grapsoidae (Aratus, Sesarma, etc.), Ocypodidae (Gelasimus,
Ocypoda), etc., and the separation of these families must doubtless be
referred to a much earlier period than the habit of leaving the water
displayed by some of their members. The arrangements connected with
aerial respiration, therefore, could not be inherited from a common
ancestor, and could scarcely be accordant in their construction. If there
were any such accordance not referable to accidental resemblance
among them, it would have to be laid in the scale as evidence against
the correctness of Darwin's views. I shall show hereafter how in this
case the result, far from presenting such contradictions, was rather in
the most complete harmony with what might be predicted from
Darwin's theory.
(FIGURE 1. Melita exilii n. sp., male, enlarged five times. The large
branchial lamellae are seen projecting between the legs.)
A second example.--We are already acquainted with four species of
Melita (M. valida, setipes, anisochir, and Fresnelii), and I can add a

fifth (Figure 1), in which the second pair of feet bears upon one side a
small hand of the usual structure, and on the other an enormous
clasp-forceps. This want of symmetry is something so unusual among
the Amphipoda, and the structure of the clasp-forceps differs so much
from what is seen elsewhere in this order, and agrees so closely in the
five species, that one must unhesitatingly regard them as having sprung
from common ancestors belonging to them alone among known species.
But one of these species, M. Fresnelii, discovered by Savigny, in Egypt,
is said to want the secondary flagellum of the anterior antennae, which
occurs in the others. From the trustworthiness of all Savigny's works
there can scarcely be a doubt as to the correctness of this statement.
Now, if the presence or absence of the secondary flagellum possessed
the significance of a distinctive generic character, which is usually
ascribed to it, or if there were other important differences between
Melita Fresnelii and the other species above-mentioned, which would
make it seem natural to separate M. Fresnelii as a distinct genus, and to
leave the others united with the rest of the species of Melita--that is to
say, in the sense of the Darwinian theory, if we assume that all the
other Melitae possessed common ancestors, which were not at the same
time the ancestors of M. Fresnelii--this would stand in contradiction to
the conclusion, derived from the structure of the clasp-forceps, that M.
Fresnelii and the four other species above-mentioned possessed
common ancestors, which were not also the ancestors of the remaining
species of Melita. It would follow:--
1. From the structure of the clasp-forceps: that M. exilii, etc. and M.
Fresnelii would branch off together from a stem which branches off
from M. palmata.
2. From the presence or absence of the secondary flagellum: that M.
palmata, etc. and M. exilii, etc. would branch off together from a stem
which branches off from M. Fresnelii.
As, in the first case, among the Crabs, a typical agreement of
arrangements produced independently of each other would have been a
very suspicious circumstance for Darwin's theory, so also, in the second,
would any difference more profound than that of very nearly allied

species. Now it seems to me that the secondary flagellum can by no
means furnish a reason for doubting the close relationship of M.
Fresnelii to M. exilii, etc., which is indicated by the peculiar structure
of the unpaired clasp-forceps. In the first place we must consider the
possibility that the secondary flagellum, which is not always easy to
detect, may only have been overlooked by Savigny, as indeed Spence
Bate supposes to have been the case. If it is really deficient it must be
remarked that I