download pdf

220
tary appearance, in the present form it was well developed, even extending con-
siderably beyond the outer. One of the two specimens (fig. 2 b) was found,
on a closer examination, to be just about to cast off its skin, and within the
pellucid envelope a quite normal Cryptoniscian larva could be discerned, exactly
agreeing with a form that I had previously not infrequently
found free in the sea
(fig. 2 c). The latter exhibits all the characters indicated by Dr. Hansen 1
) as
peculiar to the larvae belonging to the family Cryptoniscidce, and some of these
characters could also be very distinctly seen in the Microniscus stage mentioned
above (cf. the detail figures 2 b and 2 c).
From the two above given series of observations, it is thus clearly shown,
firstly, that a true Microniscus, apparently identical with the form previously
recorded by the present author as M. calani, develops from the 1st stage
of a normal Bopyrid lai'va; secondly, that another form of Microniscus, after
having attained its normal development, is transformed by a single exuviation into
the well-known 2nd larval stage, generally termed the Cryptoniscian stage ; thirdly,
that these 2 forms of Microniscus, though exhibiting a very similar appearance,
in reality belong to 2 very different families of Epicarida, the one to the Bopij-
ridce, the other to the Cryptoniscidce. In other words the name Microniscus
cannot in future be taken in the formerly-adopted sense as a generic denomi-
nation, but must be restricted to designate a transitory developmental stage of
Epicarida connecting the 2 previously-known larval stages.
It is rather difficult at present to state with certainty, to which species
of Epicarida the 2 above-mentioned Micronisci belong ; but I am much inclined
to believe that the one form will turn out to be a developing stage of Phryxus
abdominalisj and the other a similar stage of a species belonging to the genus
Podascon of Gdard and Bonnier.
Isopoda, Cumacea and Stomatopoda of the German Plankton-Expedition, p. 22.'