DEVELOPMENT OF EUPHAUSIA SUPERB A 73 



The uropods do not reach to the lateral telson spines even in the largest larvae. They 

 consist of a basal segment and two distal plates which are furnished with long setae • 

 these latter are more numerous in larger than in smaller larvae. 



Antennule. The antennules, as in the 3rd Calyptopis, are essentially made up of 

 three peduncular segments and an outer and inner flagellar segment (Figs i5f,g h j) 

 There IS an mcrease in the number of sensory filaments on the outer flagellum in the 

 larger larvae compared with the smaller ones in this group and with the 3rd Calyptopis 

 1 here are three filaments, one near the base on the inner margin and two situated ter- 

 mmally. Besides these sensory filaments there are three or four long bristles on each 

 • flagellum terminally. In the larger larvae there is also at the distal margin of the distal 

 peduncular segment a rounded protrusion immediately dorsal to the outer flagellum 

 which is armed with four small curved spines. The number of bristles on the inner mar- 

 gins of the peduncular segments has increased compared with the 3rd Calyptopis The 

 large spinous forward projection of the basal peduncular segment extends beyond the 

 distal margin of the distal peduncular segment. 



Antenna, mandible and labrum. These are essentially as in the earlier larval stages 

 (Fig. isk,l, m). 



First maxilla. The general structure is as in the 3rd Calyptopis, but there are cer- 

 tam differences in detail accompanying increase of size. Thus the outer masticatory lobe 

 has seven spines instead of five on the inner margin, and there may be an additional 

 bristle, seen in the larva with five pairs of non-setose pleopods, situated a little distant 

 from the inner margin on the surface of the lobe. The inner masticatory lobe has eight 

 spines compared with seven in the 3rd Calyptopis. The palp of this appendage is more 

 or less distinctly segmented into two, having three spines on the terminal segment and 

 two on the inner margin of the proximal. 



Second maxilla. The 2nd maxillae are as in the 2nd Calyptopis stage with five 

 lateral lobes bearing many setae and a terminal lobe with three setae. 



First thoracic limb. The ist thoracic limb is essentially as in the Calyptopis stages. 

 One is figured for comparison of size with the succeeding limbs (Fig. 16 d). 



Thoracic limbs II-VI. Unlike the ist limb the remaining thoracic limbs show a dis- 

 tinct advance in development in this stage compared with the 3rd Calyptopis. They have 

 increased greatly in length, so that they are generally as long as, or slightly longer than, 

 the ist thoracic. In the larvae examined an indication is given of the irregularity in the 

 development of appendages in individual larvae. Thus the larva with only two pairs of 

 pleopods has the thoracic limbs (Fig. i6«) rather more advanced than the larva with three 

 pairs of pleopods (Fig. i6b). This is probably exceptional, and in the normal course one 

 would expect to find the longer and more developed thoracic appendages occurring in 

 larvae with the larger number of pleopods. The segmentation of the endopod is more 

 distinct in larvae with four or five pleopods, so that whereas in the smaller ones the an- 

 terior limbs show only the first signs of incipient segmentation and the posterior ones 

 none at all, in the larva with five pleopods (Fig. ib d) the anterior limbs are five- 

 segmented and thoracic limb VI has three segments. The segmentation is difficult to 



