"The peculiarities in which the Zoeae of the Crabs, the Porcellanae, the
Tatuira, the Hermit Crabs, and the Prawns with Zoea-brood agree, and by
which they are in common distinguished from the larvae of Peneus
produced from Nauplii, forces us (it might be said) to the supposition
that the common ancestor of these various Decapods quitted the egg in a
similar Zoea-form. But then neither Peneus with its Nauplius-brood, nor
even apparently the Palinuri could be referred back to this ancestor.
The mode of development of Peneus and Palinurus, as also several
peculiar larvae of unknown origin, but which are in all probability to
be attributed to Macrurous Crustacea, necessitate on the contrary the
opposite supposition, namely, that the different groups of the Macrura
have passed from their original to their present mode of development
independently of each other and also independently of the Crabs." To
this we may answer that the occurrence of the Zoea-form in all the
above-mentioned Decapoda, its existence in Peneus during the whole of
that period of life which is richest in progress and in which the wide
gap between the Nauplius and the Decapod is filled up, its recurrence
even in the development of the Stomapoda, the occurrence of a larval
form closely approaching the youngest Zoea of Peneus in the Schizopod
genus Euphausia, and the reminiscence of the structure of Zoea, which
even the adult Tanais has preserved in its mode of respiration,--all
indicate Zoea as one of those steps in development which persisted as a
permanent form throughout a long period of repose, perhaps through a
whole series of geological formations, and thus has also made a deeper
impression upon the development of its descendants, and formed a firmer
nucleus in the midst of other and more readily effaced young states. It
cannot, therefore, surprise us that in transitions from the original
mode of metamorphosis to direct development, even when produced
independently, the larval life commences in the same way with this