22 G. O. Sars. 



other 2 eminences, is the dorsal. The anterior eminence is 

 the antennula, the middle one the antenna, and the posterior 

 the mandibular leg. Gradually the eminences become more 

 prominent, and, as it were, detach themselves from the 

 sides of the body, so as at last to be only connected with 

 it ventrally (see fig. 12). At first the embryo is enclosed 

 within the vitelline membrane; but this membrane is soon 

 ruptured (see fig. 13), whereby the embryo is freely 

 suspended within the hollow of the sphere. The Nauplian 

 limbs now admit of being gradually extended, and at last 

 project freely from each side of the body (see PL 3, fig. 1). 

 They now begin to move in a somewhat irregular manner, 

 which causes the embryo to revolve within the cavity 

 of the sphere. Soon the movements become more energetic, 

 and at last cause the rupture of the thin external coating 

 of the sphere, whereupon the young individual escapes in a 

 very imperfect condition, as a rather simple Nauplius, to be- 

 gin its lengthy larval development. 



VI. 

 The Nauplius. 



On its escape from the oosphère, the Nauplius (PI. 3, 

 fig. 2) has a length of about 0.45 mm., and still exhibits a 

 rather clumsy appearance, the body being almost globular 

 in form and the Nauplian limbs still rather short and thick, 

 with only a restricted number of short, simple bristles at 

 their tips. Ventrally, near the posterior extremity, a slight 

 depression may be traced, indicating, it would seem, the 

 place where the gastrula-mouth had been formed; but no 

 true oral aperture or any mouth-organs are as yet visible. 



