24 G- 0- S ars - 



a separate ledge of the inner edge. The inner ramus has 

 only 3 such setæ, 2 apical and one lateral. The mandibular 

 legs (fig. 5) resemble the antennæ in structure, but are con- 

 siderably shorter, and without the lateral seta on the outer 

 ramus. They are also very mobile, assisting the antennæ 

 in the locomotory motion, which is effected by abrupt jerks 

 produced by rhythmical strokes of both these appendages 

 from before backwards. The body, as also the above- 

 described limbs, is still filled with a somewhat opaque cellular 

 mass, and no distinct internal organs are as yet visible, though 

 the cells are seen to arrange themselves in several sets, to 

 form the different tissues of the body. Along the dorsal 

 face, however, several muscular fibres are already clearly 

 distinguishable, joining the limbs from behind (see fig. 3). 

 The Nauplius, though moving freely in the water, still 

 exhibits an evident embryonal character in its incapacity 

 to take in nourishment from the surrounding medium, 

 This becomes only possible after the Nauplian skin is cast 

 off, and the larva has entered the next stage, that of the 

 Metanaplius. Some- time before this proceess takes place, 

 the formation of the mouth, and the first traces of the oral 

 parts may be observed, on viewing the Nauplius from the 

 ventral face (see fig. 4); but all these parts are in reality 

 formed inside the Nauplian skin, which passes without any 

 interruption over them. The Nauplius of the Euphausiidæ, 

 accordingly, represents more properly an earlier stage of 

 development than that of the Copepodaand Cirripedia, in which 

 the mouth is at once formed, and a simple, but rather effec- 

 tive contrivance for carrying the food in the mouth exists 

 'in the so-called masticatory processes of the antennæ, which 

 are wholly wanting in the Nauplius of the Euphausiidæ. 



