Euphausiidæ. 23 



In this stage, however, the Nauplius remains but a very- 

 short time. It soon casts off its skin, and now appears 

 (see fig. 3) as a more regular and much more agile Nau- 

 plius, though still of a very simple stucture, as compared 

 with the usual Nauplii of Copepoda and Cirripedia. The 

 body, which now measures about 0.55 mm. in length, has 

 assumed a regular oval or elliptical form, with both 

 extremities nearly alike and narrowly rounded; from the 

 posterior one 2 small hairs are seen to project. In this 

 stage too, no trace of a mouth or of oral parts is to be 

 found, and even the simple eye or ocellus, which in other 

 Nauplii is so very conspicuous, scarcely admits of being 

 distinctly traced, though it may probably be in process of 

 formation. The Nauplian limbs, on the other hand, show 

 themselves to be much more fully developed than in the 

 preceding stage, and are rather mobile. They all issue 

 somewhat ventrally from the anterior half of the body, and, 

 as a rule, radiate in different directions. The antennulæ 

 are generally extended straight in front, though they admit 

 of being moved more or less laterally. They are narrow 

 cylindric in form, very slightly curved, and about half as 

 long as the body, being still inarticulate, and provided at 

 the tip with only 2 unequal bristles and a minute spinule. 

 The antennæ are somewhat longer than the antennulæ, and 

 are generally extended laterally ; but as they are very mobile, 

 they may point now more anteriorly, now more posteriorly. 

 They each consist of a cylindrical scape, which at the base 

 exhibits several annular instrictions, and of 2 rami, the 

 outer or upper of which is somewhat larger than the inner, 

 both being still inarticulate and imperfectly defined from 

 the scape. The outer ramus carries 4 strong, ciliated 

 natatory setæ, 3 of which issue from the tip, the 4th from 



