48 



G. O. SÅRS. 



[No. L 



ridge is the free edge of the developing snell, or carapace. The 

 embryonic cuticle (l) can be now distiuctly seen enveloping the body 

 of the embryo, inside the vitelline membrane (v), especially when 

 the embryo is turned so as to afford a lateral aspect (fig. 8). 

 Moreover, viewed in that position, the opaque greenish yolk-mass 

 is found to have retired some distance from the head, whereas 

 it would still seem to lie in close contact with the dorsal sur- 

 face of the embryo. 



In the next stage, represented in figs. 9 — 11, the chorion has 

 been completely east off, and now the vitelline membrane (v) 

 invests the embryo but loosely, a considerable quantity of a 

 clear fluid having accumulated between that membrane and the 

 embryonic cuticle, the latter of which (1) still closely envelop the 

 body, arching over the developing legs. The body of the embryo 

 has assumed a more oblong-oval form, and exhibits in a lateral 

 aspect (fig. 11) a distinct dorsal curvature, a råtner deep sinus 

 occurring in the middle of the dorsal side of the trunk, arched 

 over by the embryonic cuticle (Z). The cephalic part of the body 

 is very distinctly defined, and projects both inferiorly and 

 superiorly as a somewhat club-shaped prominence, the former (X) 

 representing the labrum, the latter (x) the occipital process. 

 The antennulæ (a J ) have increased in size, forming a pair of 

 well-defined rounded mammillar prominences slightly projecting 

 in front; the antennæ (a 2 ), too, are considerably more elongated 

 than in the preceding stage. The mandibles (M), on the other 

 hand, would seem to have retained their original form and size 

 nearly unchanged, though somewhat more withdrawn from the 

 anterior part of the head. Behind the latter organs, both pairs 

 of maxillæ (m) are now distinctly vlcible as small densely crowded 

 prominences. The eight pairs of pedal prominences are more 

 distinctly defined, exhibiting a slightly lobular form, and behind 

 them we have another pair in development. The posterior extremity 

 of the body is still, however evenly rounded, without any projec- 

 tions. The edges of the developing shell (C) now admit of being 

 distinctly traced all round, meeting in the middle of the dorsal 

 surface, where they form together a broad angular sinus (see fig. 9j. 



