attention to these animals, and a careful examination proved that these
Isopods have preserved, more truly than any other adult Crustacea, many
of the most essential peculiarities of the Zoeae, especially their mode
of respiration. Whilst in all other Oniscoida the abdominal feet serve
for respiration, these in our cheliferous Isopod (Figure 2) are solely
motory organs, into which no blood-corpuscle ever enters, and the chief
seat of respiration is, as in the Zoeae, in the lateral parts of the
carapace, which are abundantly traversed by currents of blood, and
beneath which a constant stream of water passes, maintained, as in Zoeae
and the adult Decapoda, by an appendage of the second pair of maxillae,
which is wanting in all other Edriophthalma.

For both these discoveries, it may be remarked in passing, science is
indebted less to a happy chance than immediately to Darwin's theory.

Species of Peneus live in the European seas, as well as here, and their
Nauplius-brood has no doubt repeatedly passed unnoticed through the
hands of the numerous naturalists who have investigated those seas, as
well as through my own,* for it has nothing which could attract
particular attention amongst the multifarious and often wonderful
Nauplius-forms. (* Mecznikow has recently found Naupliiform
shrimp-larvae in the sea near Naples.) When I, fancying from the
similarity of its movements that it was a young Peneus-Zoea, had for the
first time captured such a larva, and on bringing it under the
microscope found a Nauplius differing toto coelo from this Zoea, I might
have thrown it aside as being completely foreign to the developmental
series which I was tracing, if the idea of early Naupliiform stages of
the higher Crustacea, which indeed I did not believe to be still extant,
had not at the moment vividly occupied my attention.