numerous openings far into the abdomen, we must unhesitatingly regard
the heart of the Amphipoda as the primitive form of that organ in the
Edriophthalma. As, moreover, in these animals the blood flows from the
respiratory organs to the heart without vessels, it is very easy to see
how advantageous it must be to them to have these organs as much
approximated as possible. We have reason to regard as the primitive mode
of respiration, that occurring in Tanais (vide supra). Now, where, as in
the majority of the Isopoda, branchiae were developed upon the abdomen,
the position and structure of the heart underwent a change, as it
approached them more nearly, but without the reproduction of a common
plan for these earlier modes of structure, either because this
transformation of the heart took place only after the division of the
primary form into subordinate groups, or because, at least at the time
of this division, the varying heart had not yet become fixed in any new
form. Where, on the contrary, respiration remained with the anterior
part of the body,--whether in the primitive fashion of Zoea, as in the
Tanaides, or by the development of branchiae on the thorax, as in the
Amphipoda,--the primitive form of the heart was inherited unchanged,
because any variations which might make their appearance were rather
injurious than advantageous, and disappeared again immediately.

I close this series of isolated examples with an observation which
indeed only half belongs to the province of the Crustacea to which these
pages ought to be confined, and which also has no further connexion with
the preceding circumstances than that of being an "intelligible and
intelligence-bringing fact" only from the point of view of Darwin's
theory. To-day as I was opening a specimen of Lepas anatifera in order
to compare the animal with the description in Darwin's 'Monograph on the
Subclass Cirripedia,' I found in the shell of this Cirripede, a
blood-red Annelide, with a short, flat body, about half an inch long and