SCHIZOPODA. 255 



the formation 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 Metanaupllus gives rise through further moults to the series 



of Galyptopis stages (Fig. 117 J? 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 two 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 (the 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 (4, o) and 



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



in their form considerable agreement with the Phyllopodan limbs. 



The first maxilla (4), 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 (1) has the character of a biramose swimming 



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



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



rudiments of the other thoracic segments can already be distinctly 



seen (Fig. 117 B, th), while the abdomen (ab) 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 6 ) can be recognised. The cephalo-thoracic 



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



great development. In Euphausia 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 Cypridlna and 



Halocypris. In other genera (Nyctiphanes) 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 



