8o DISCOVERY REPORTS 



basal portion greatly broadened as in subsequent stages. The telson is from 2| to 3 times 

 as long as its greatest width. The uropods extend to, or a very little way beyond, the 

 lateral spines of the telson. The setae on the margins of the exopod and endopod are in- 

 creased in number — as many as twelve being found on the outer ramus and ten on the 

 inner ramus (Fig. 17/, |', h). 



Antennule. The antennules are not altered in general structure, consisting as they 

 do of three peduncular segments with two flagella distally (Fig. i'] c, d, e). The latter 

 are unsegmented except in the largest larvae included in this stage (Fig. 17 e); in these 

 the flagella may show faint indications of division into a proximal and distal segment. 

 The sensory filaments of the flagella are situated away from the tip of the inner side of 

 the outer flagellum. The forward spinous lateral projection of the basal peduncular seg- 

 ment does not extend as far as the distal margin of the distal peduncular segment. As in 

 the previous stage it is armed with spinules along the inner margin. There are also 

 several spinules around the base of this spine on the basal peduncular segment. The 

 flagella are shorter than the combined lengths of the two distal peduncular segments. 



Antenna. The antennae are still unchanged (Fig. 177). 



Mandible. In this stage the first signs of the changes in the mandible leading to the 

 adult form become noticeable. The palp tends to be more elongate in the larger larvae ; 

 for example, in the larva with all pleopods setose it is an unsegmented digitiform pro- 

 cess. The specimen figured shows segmentation within the integument and a long 

 spine embedded in the soft tissues (Fig. 17 k). In the smaller larvae the palp is a short 

 conical process similar to that found in earlier stages. 



There are alterations in the tooth portion of the mandible which are most pronounced 

 in the largest larvae. Sars (1885), referring to Nyctiphanes australis (p. 153), says in his 

 description of the Calyptopis mandible : 



The armature of the cutting edges is well developed though somewhat dissimilar to that in the 

 adult animal, resembling rather the armature found in some Mysidae. As it occurs in the latter the 

 anterior part is divided into several strong, and very closely arranged, teeth forming together two 

 partly superposed portions which in the two mandibles exhibit a somewhat different shape. Between 

 this dentate part and the molar protuberance occurs a short dentiform projection, and at the base of 

 the latter is affixed on both mandibles a very peculiar narrow plate expanded at the extremity and 

 having the apical edge finely denticulate. This plate, wanting entirely in the adult animal, would 

 appear to be movably connected with the mandible since it is very easily disengaged. 



That part of the incisor process which could in the earlier stages be recognized as a 

 pedunculated projection bearing small denticulations on the inferior border distally 

 becomes reduced in size in the smaller larvae belonging to this stage (Fig. 186) and in 

 the larger disappears altogether. The lacinia mobilis also is less conspicuous in the 

 larger larvae of this furcilia stage. 



First maxilla. The general structure is as in 3rd Calyptopis, that is, consisting of a 

 palp, outer and inner masticatory lobe and an exognath (Fig. 17ft). The advance in 

 development from the previous stage is evident in the palp, which is now composed of 

 a single segment, and in the masticatory lobes, where an increase in the number of 

 spines has taken place. In the larva with three pairs of setose pleopods the outer lobe 



