Fig. 36. Embryo of Ligia in the egg, magnified. D. yelk; L. liver. Fig. 37. Maggot-like larva of Ligia, magnified. R remains of the egg-membrane. We see on the lower surface, from before backwards:--the anterior and posterior antennæ, the mandibles, the anterior and posterior maxillæ, maxillipedes, six ambulatory feet, the last segment of the middle-body destitute of appendages, five abdominal feet, and the caudal feet. Fig. 36. Embryo of _Ligia_ in the egg, magnified. _D._ yelk; _L._ liver. Fig. 37. Maggot-like larva of _Ligia,_ magnified. _R_ remains of the egg-membrane. We see on the lower surface, from before backwards:—the anterior and posterior antennæ, the mandibles, the anterior and posterior maxillæ, 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. 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 Bopyridæ,—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 (Fig. 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_).[1] That the last pair of feet of the thorax is wanting in the young of the Wood-lice (_Porcellionides,_ M.-Edw.) and Fish-lice (_Cymothoadiens,_ M.-Edw.) has already been noticed by Milne-Edwards. This applies also to the Box-Slaters (_Idothea_), to the viviparous Globe-Slaters (_Sphæroma_) and Shield-Slaters (_Cassidina_), to the Bopyridæ (_Bopyrus, Entoniscus, Cryptoniscus,_ n.g.), and to the Cheliferous Slaters (_Tanais_), and therefore probably to the great majority of the Isopoda. All the other limbs are usually well developed in the young Isopoda. In _ Tanais_ alone, all the abdominal feet are wanting (but not those of the tail); they are developed simultaneously