backwards:--the anterior and posterior antennae, the mandibles, the
anterior and posterior maxillae, maxillipedes, six ambulatory feet, the
last segment of the middle-body destitute of appendages, five abdominal
feet, and the caudal feet.)

The young animal, when it begins to take care of itself, resembles the
old ones in almost all parts, except one important difference; it
possesses only six, instead of seven pairs of ambulatory feet; and the
last segment of the middle-body is but slightly developed and destitute
of appendages. It need hardly be mentioned that the sexual peculiarities
are not yet developed, and that in the males the hand-like enlargements
of the anterior ambulatory feet and the copulatory appendages are still
deficient.

(FIGURE 38. Embryo of a Philoscia in the egg, magnified 25 diam.)

To the question, how far the development of Ligia is repeated in the
other Isopoda, I can only give an unsatisfactory answer. The curvature
of the embryo upwards instead of downwards was met with by me as well as
by Rathke in Idothea, and likewise in Cassidina, Philoscia, Tanais, and
the Bopyridae,--indeed, I failed to find it in none of the Isopoda
examined for this purpose. In Cassidina also the first larval skin
without appendages is easily detected; it is destitute of the long tail,
but is strongly bent in the egg, as in Ligia, and consequently cannot be
mistaken for an "inner egg-membrane." This, however, might happen in
Philoscia, in which the larval skin is closely applied to the
egg-membrane (Figure 38), and is only to be explained as the larval skin
by a reference to Ligia and Cassidina. The foliaceous appendage on the
back has long been known in the young of the common Water Slater
(Asellus).* (* Leydig has compared this foliaceous appendage of the