SCHIZOPODA. 255 



the fonnation of lobes is evident, while, near the Nauplius eye, a 

 paired frontal organ (fs) has developed, similar to that already 

 described in the Phyllopod larva. 



The MetanaupUus gives rise tlirongh further moults to the series 

 of Calyptopis stages (Fig. 117 5 and C), which are characterised by 

 the development of the six most anterior pairs of limbs, and of the 

 long posterior (thoraco-abdominal) region of the body. The tAvo pairs 

 of antennae still retain essentially the Nauplius character, although 

 they are now jointed. The first antenna now exhibits a three-jointed 

 shaft, at the end of which two short processes (tlie rudiments of the 

 future flagella) are inserted. In the second antenna, at the end of 

 the exopodite which is covered with setae, a distinct segmentation 

 into closely-crowded rings is evident. The two maxillae (-^, 5) and 

 the first maxillipede (/) appear as richly-lobed appendages, showing 

 in their form considerable agreement with the Phyllopodan limbs. 

 The first maxilla (-^), besides its two masticatory blades and its 

 endopodite, shows a short truncated portion bearing setae (exopodite), 

 the rudiment of the future fan-like plate. In the second maxilla {5) 

 the exopodite is in quite a rudimentary condition, while, on the inner 

 side of the protopodite, four masticatory processes have developed. 

 The first maxillipede (7) has the character of a biramose swimming 

 limb (especially in Ntjdiphanes). At the beginning of the thoraco- 

 abdoraen, which lies behind these appendages, the closely-crowded 

 rudiments of the other thoracic segments can already be distinctly 

 seen (Fig. 117 Z?, th), while the abdomen {ah) still appears un- 

 segmented. The posterior end of the abdomen has already been 

 transformed into the middle plate of the caudal fin, and is beset 

 with strong spines along its posterior edge. In front of the anal 

 aperture the first rudiments of the lateral parts of the caudal fin 

 (sixth pair of pleopoda, a^) can be recognised. The cephalo-thoracic 

 shield, which covers the anterior part of the body, has undergone 

 o'reat development. In Euphauda it is distinguished by the presence 

 of an unpaired dorsal spine directed backwards, by the delicate 

 dentation of its edges, and by a notch in its ventral margin which 

 recalls the excavation in the edges of the shell in Cijpridina and 

 Halorypris. In other genera {Nydiplianes) the shell has no dorsal 

 spine and the margins are not toothed ; there are also only very 

 indistinct lateral notches in the margin of the shell. The internal 

 organs, which should be noticed at this stage, are the gradually 

 developing paired rudiments of the eye, the hepatic outgrowths of 

 the alimentary canal, and the short sac-like heart which is continuous 



