Fig. 50. Foot of the second pair ('second pair of gnathopoda') of the male of Orchestia Tucurauna, magnified. Fig. 51. Foot of the second pair ('second pair of gnathopoda') of the female of Orchestia Tucurauna, magnified. Fig. 52. Male of a Bodotria, magnified. Note the long inferior antennæ, which are closely applied to the body, and of which the apex is visible beneath the caudal appendages. Fig. 50. Foot of the second pair (“second pair of gnathopoda”) of the male of _Orchestia Tucurauna,_ magnified. Fig. 51. Foot of the second pair (“second pair of gnathopoda”) of the female of _Orchestia Tucurauna,_ magnified. Fig. 52. Male of a _Bodotria,_ magnified. Note the long inferior antennæ, which are closely applied to the body, and of which the apex is visible beneath the caudal appendages. Next to the extensive sections of the Stalk-eyed and Sessile-eyed Crustacea, but more nearly allied to the former than to the latter, comes the remarkable family of the _ Diastylidæ_ or _Cumacea._ The young, which Kröyer took out of the brood-pouch of the female, and which attained one-fourth of the length of their mother, resembled the adult animals almost in all parts. Whether, as in _Mysis_ and _Ligia,_ a transformation occurs within the brood-pouch, which is constructed in the same way as in _Mysis,_ is not known.[7] The caudal portion of the embryo in the _Diastylidæ,_ as I have recently observed, is curved upwards as in the Isopoda, and the last pair of feet of the thorax is wanting. Equally scanty is our knowledge of the developmental history of the Ostracoda. We know scarcely anything except that their anterior limbs are developed before the posterior one (Zenker). The development of _Cypris_ has recently been observed by Claus:—“The youngest stages are shell-bearing Nauplius-forms.” [1] Leydig has compared this foliaceous appendage of the Water Slaters with the “green gland” or “shell-gland” of other crustacea, assuming that the green gland has no efferent duct and appealing to the fact that the two organs occur “in the same place.” This interpretation is by no means a happy one. In the first place we may easily ascertain in _Leucifer,_ as was also found to be the case by Claus, that the “green gland” really opens at the end of the process described by Milne-Edwards as a “tubercule auditif” and by Spence Bate as an “olfactory denticle.” And, secondly, the position is about as different as it can well be. In the one case a paired gland, opening at the base of the posterior antennæ, and therefore on the lower surface of the _second_ segment; in the other an unpaired structure rising in the median line of the back _behind the seventh segment,_ (“behind the boundary line of the first thoracic segment,” Leydig).