6 G. O. Sars. 



The head is produced ventrally (see fig. 2) into a large, 

 shield-like plate extending posteriorly beyond the limit of 

 the 2 body-divisions, and representing the greatly developed 

 anterior lip or labrum. It covers over the place, where the 

 oral opening is to be formed, and exhibits a regular oval 

 form, with the edges evenly curved. 



Ot the 3 pairs of Nauplian limbs, as above stated, those of the 

 anterior one, the antennulæ, are still quite rudimentary, only 

 forming, on each side of the frontal part, a very small, knob- 

 like prominence tipped by a slender and delicate sensory 

 bristle. The 2nd pair of Nauplian limbs, the antennæ, are, 

 on the other hand, very largely developed, constituting the 

 chief locomotory organs of the larva. They originate from 

 the sides of the [anterior division, and are extended later- 

 ally as a pair of powerful arms, but being very mobile, 

 they admit of being bent, now anteriorly, now posteriorly, 

 and it is indeed by such movements that the animal is 

 propelled through the water. The proximal part of these 

 limbs forms a rather thick and very flexible scape, from the 

 base of which, somewhat ventrally, a conical process issues, 

 pointing posteriorly, and tipped by a single, spine-like bristle. 

 At the end of the scape, moreover, a strong posteriorly 

 curving seta is seen to originate. The distal part of the 

 limb is represented by 2 unequal rami issuing close together 

 from the tip of the scape. The outer ramus is the larger, 

 and of a somewhat fusiform shape, being provided with 4 

 strong setæ, 2 of which issue from the tip, the other 2 from 

 slight notches on the inner edge. The inner ramus is nearly 

 cylindric in form, and carries on its tip 3 strong setæ ac- 

 companied by a small, dentiform process. 



The 3rd pair of Nauplian limbs, the mandibular feet, 

 originate on each side of the median instriction of the body 



