On the Development of Cumaeea. 



(PI. LXIX.) 



Kr0yer was the first to state that the young of Cumaeea do not undergo 

 any metamorphosis, but on leaving the mother have essentially the same appearance 

 as the adults. A closer investigation of the embryonal development was subse- 

 quently instituted by Dr. A. Dohrn, who figured several stages of Cuvnopsis 

 Goodsiri, and pointed out the great resemblance, at least in the earlier stages, 

 to the development of Isopoda (Asellus). I have myself studied the development 

 in the following genera: Lamprops, Leucon, Diaxtt/lix and Pscudocuma. In all 

 these genera it is essentially alike, and it is sufficient therefore to describe 

 it in one of them, viz., Diastylls. 



The ova, immediately after they have left the ovarial sacs, are globular in 

 form (see fig. 1), and surrounded by a very thin filmy membrane, which in some 

 places is closely applied to the ovum, in others stands away from its surface. 

 They undergo, as in most other Crustacea, a superficial cleavage, whereby a 

 peripheric layer of clear nucleated cells is formed, surrounding the coarsely 

 granular opaque yolk. In one place these cells increase considerably in number, 

 forming a conspicuous thickening of the peripheric cell-layer. This part repre- 

 sents the ventral face of the embryo, and extends like a broad band around the 

 greater part of the ovum. At the same time the central yolk-mass seems to 

 arrange itself with tolerable regularity in relation to this thickened part of the 

 surface, forming 2 conspicuous rounded lateral expansions (see figs. 2 & 3). In 

 the middle, opposite the thickened part of the peripheric layer, appears a slight 

 insinuation of the surface (see fig. 4, f) ; this becomes gradually deeper in the 

 course of the development, and represents the dorsal cleft separating the two 

 extremities of the embryo. The latter of course originally exhibits, like the 

 embryos of Isopoda, a strong dorsal curvature. The first indications of all the 

 limbs belonging to the anterior division of the body, with the exception of the 

 last pair, are very soon to be traced along the thickened ventral face of the 



