SERGESTIDAE. 259 



long rostrum (r) ; this carries on its posterior margin one unpaired 

 dorsal and two somewhat longer lateral spines. The posterior region 

 of the body has developed into a large thoraco-abdomen, the most 

 posterior end of which is transformed into the middle plate (telson) 

 of the caudal fin, and is provided with strong spines. Behind the 

 second maxillipede, four more segments have become distinct — that 

 carrying the third pair of maxillipedes (Fig. 119 A, mp") and 

 those carrying the three anterior pairs of ambulatory limbs (t l -t z ). 

 The heart (h) and the hepatic outgrowths of the intestinal canal (/) 

 have developed. The first antenna (a') now consists of two joints 

 only, a long basal and a short terminal joint beset with setae ; the 

 second antenna (a") has essentially the same shape as in the preceding 

 stage ; it has an exopodite of several joints beset with many setae 

 and a simpler endopodite ; it still functions as the chief locomotory 

 organ of the larva. The mandible (Fig. 119 D, md) now consists 

 exclusively of a masticatory blade toothed along its inner edge. All 

 trace of the palp found on the mandible at earlier stages is now lost. 

 The two pairs of maxillae already foreshadow their adult form. The 

 first maxilla (Fig. 119 5) shows, on the inner side of the protopodite, 

 two projecting masticatory blades, a short, two-jointed endopodite, 

 and a truncated exopodite beset with feathered setae. The second 

 maxilla (Fig. 119 C) is principally distinguished by the large number 

 of masticatory processes borne on its inner border. The two pairs 

 of maxillipedes (Fig. 119 D, mf, mf") are shaped like biramose 

 swimming limbs with long endopodites composed of several joints 

 and short, unjointed exopodites. In the maxillary region a shell- 

 gland is seen developing. 



Later Protozoaea stages (Fig. 1 1 9 D), which correspond to Dana's 

 Erichthina demissa, are distinguished by the commencing develop- 

 ment of the paired eyes (o), as well as by the further advance of 

 segmentation in the thoraco-abdomen. At the antero-lateral margin 

 of the dorsal shield a swelling becomes apparent, within which an 

 accumulation of pigment denotes the rudiment of the paired eye. 

 Among the new segments that have appeared in the posterior 

 region of the body are those carrying the fourth ambulatory limbs 

 (t 4 ) and the four anterior abdominal segments (1-4). The last 

 thoracic segment (that carrying the fifth pair of ambulatory limbs) 

 never attains distinct development in Lucifer. The abdomen is 

 not yet segmented. 



The next stage (Fig. 119 E) is marked by the complete segmenta- 

 tion of the abdomen, and must therefore be called a Zoaea stage. 



