DEVELOPMENT OF EUPHAUSIA SUPERB A 8i 



has eight marginal spines and one submarginal ; the inner lobe spine number is un- 

 changed. In the larva with four pairs of setose pleopods there are at least nine marginal 

 spines on the outer masticatory lobe and a similar number on the inner. In the larva 

 with all pleopods setose there are only eight marginal bristles on the outer masticatory 

 lobe, but there are three submarginal bristles; on the inner there are nine marginal 

 bristles. 



Second maxilla. The 2nd maxillae are as in the previous stage (Fig. 17 m). 



First thoracic limb. In the smaller larvae in this group the ist thoracic appendage 

 (Th. I) is as in previous stages, but in the larger larvae there is an advance in develop- 

 ment marked by the elongation of the inner ramus and by its further segmentation into 

 more than two. The endopod is never more than about twice as long astheexopod(Figs. 

 iS c, d, e). 



Thoracic limbs II-VII. The thoracic limbs II-VI are much larger than Th. I. 

 Also in this stage the flexion of the limbs which is found in adults becomes noticeable ; 

 that is to say, in the endopod the two proximal segments are directed forwards and 

 downwards, and the three distal segments reflexed so that they point downwards and 

 backwards. Of the larvae examined that having three pairs of setose pleopods has the 

 thoracic limbs IV-VI of the form shown in Fig. 18 c. The 2nd thoracic limb endopod is 

 longer than the ist but shorter than Th. Ill or Th. IV which are the most developed 

 of these appendages. The fifth limb endopod is indistinctly five-segmented, and the 

 sixth, which is much the shortest, is still "sausage-shaped" and not so densely setose 

 as the more anterior limbs. The setae on the endopods, which are chiefly situated 

 along the inner margin of the limb, are of two kinds — short plumose setae projecting 

 inwards, and longer plumose setae directed anteriorly. This applies to the proximal 

 segments of the endopod; the distal three segments are not so heavily setose. The 

 exopods, with the exception of the Vlth, are more lamellar in form than in the pre- 

 vious stage ; setae are present on the outer and inner margins as well as on the tips. In 

 Th. Ill, IV and V the exopod shows the beginning of differentiation into two portions, 

 a distal natatory part and, proximally, a strongly muscular portion. The distinction is 

 noticeable in the outer margin by the formation of a shoulder-like projection about the 

 middle of this edge, and on the inner margin by a curved projection near the base. 



In the larvae with four pairs of setose pleopods there is an increase in the number of 

 setae on exopods and endopods (Fig. 18 d). The endopod of Th. VI is segmented into 

 four and the exopod is more lamellar in form than in the smaller larva with three pairs 

 of pleopods. Situated behind Th. VI is a very small inconspicuous protrusion — the 

 first rudiment of Th. VII. 



In the largest larva — that having five pairs of setose pleopods — the endopods of the 

 limbs II-VI are all distinctly five-segmented and the exopods are clearly divided into 

 two portions, a distal natatory part and a proximal muscular part (Fig. 18 e). Setae 

 extend along both the outer and inner margins to the projections on these described 

 above. Setae on the endopod are greatly developed. Fig. 18 e shows the inner margin 

 of Th. V to illustrate the arrangement of the two sets of setae found in the two proximal 



