two pairs of thick ensiform appendages make their appearance at the
opposite end of the body, and behind these a pair of tubercles which are
easily overlooked. These are the antennae and mandibles. The
egg-membrane now bursts, before any internal organ, or even any tissue,
except the cells of the cutaneous layer, is formed. The young animal
might be called a Nauplius; but essentially there is nothing but a rough
copy of a Nauplius-skin, almost like a new egg-membrane, within which
the Mysis is developed. The ten pairs of appendages of the fore-
(maxillae, maxillipedes) and middle-body make their appearance
simultaneously, as do the five pairs of abdominal feet at a later
period. Soon after the young Mysis casts the Nauplius-envelope it quits
the brood-pouch of the mother.* (* Van Beneden, who regards the
eye-peduncles as limbs, cannot however avoid remarking upon Mysis: "Ce
pedicule n'apparait aucunement comme les autres appendices, et parait
avoir une autre valeur morphologique.")

For some time, owing to an undue importance being ascribed to the want
of a particular branchial cavity, Mysis, Leucifer, and Phyllosoma were
referred to the Stomapoda, which are now again limited, as originally by
Latreille, to the Mantis-shrimps (Squilla), the Glass-shrimps
(Erichthus) and their nearest allies. Of the developmental history of
these we have hitherto been acquainted with only isolated fragments. The
tracing of the development in the egg is rendered difficult by the
circumstance, that the Mantis-shrimps do not, like the Decapoda, carry
their spawn about with them, but deposit it in the subterranean passages
inhabited by them in the form of thin, round, yellow plates. The spawn
is consequently exceedingly difficult to procure, and unfortunately it
becomes spoilt in a day when it is removed from its natural hatching
place, whilst on the contrary the progress of development may be
followed for weeks together in the eggs of a single Crab kept in