SERGESTIDAE. 265 



Protozoaea stage of Lucifer, from which, however, it is distinguished by the 

 compact form of its body, the early development of the stalked eyes, and 

 the appearance of the third pair of maxillipedes (mf"). The seven anterior 

 pairs of limbs agree very closely in structure with those of the Protozoaea 

 stage of both Lucifer and Penaeus. The first antenna (a') especially shows a 

 segmentation of the base into live joints which recurs in Penaeus. The 

 mandibles have no palps, the first maxilla (mx') has its exopodite developed 

 as a fan-like plate, such an exopodite again being found on the long leg-like 

 second maxilla (mx"). At the base of the latter, Claus found the coiled shell- 

 gland (sd). The three pairs of maxillipedes {mf'-mf") are biramose limbs, the 

 third pair, however, being somewhat small. Behind these are found the five 

 narrow segments which later carry the ambulatory limbs, while the abdomen 

 still appears altogether unsegmented. The latter terminates in a plate which 

 runs out into prongs, and is here much more marked than in Lucifer. This 

 terminal part seems to find its homologue in the anal segment of the Phyllopoda 

 with its two furcal processes. A marked feature of this stage is the great develop- 

 ment of the movable stalked eyes and the development of protective processes 

 on the broadened dorsal shield. There are here one anterior rostral spine 

 starting from a broad base, one dorsal and two lateral spines, each of which 

 appears branched through the formation of secondary processes. These spines 

 no doubt correspond to the much shorter ones of the Lucifer larva, with which 

 they agree in position. 



The Zoaea which emerges from the stage just described (Elaphocaris) is still 

 more abundantly armed with spines. The frontal, dorsal, and lateral spines 

 have, greatly increased in size. The frontal spine has become comparatively 

 slender, and a pair of branched antero-lateral spines have developed on its 

 base. The separate segments of the abdomen also, which are now distinct 

 (except that the sixth segment is still indistinguishable from the forked telson), 

 are also well armed with lateral spines. While the anterior limbs, including 

 the three pairs of maxillipedes, have the same character as in the former stage, 

 only the rudiments of the biramose limbs are to be recognised on the five 

 following thoracic segments. The sixth pair of pleopoda has also appeared. 



In the transition to the Mysis stage (Acanthosoma, Fig. 121 B) the complicated 

 armature of the dorsal shield is lost, only the basal portions of the branched 

 processes found in the Elaphocaris being retained as short s] tines, but the spines 

 on the abdomen are still retained. The furcal processes of the telson are 

 also reduced to two short spines projecting backwards. Significant changes are 

 found in the development of the limbs. The first antenna in younger Acantho- 

 foma has a long, still unjointed protopodite (provided with a basal toothed 

 process) and two short terminal processes which appear to be the rudiments of 

 the principal and accessory flagella of later stages. In the second antenna (a") 

 the formerly many-jointed exopodite is transformed into a rod-like appendage, 

 while the endopodite has developed into a long flagellum. The two pahs of 

 maxillae still show the character described for the earlier stage. The anterior 

 niaxillipede is remarkable for the reduction of its exopodite ; but the seven 

 following pairs of limbs (the two remaining maxillipedes and the limbs which 

 have developed from the five rudiments on the thoracic segments) are changed 

 into conspicuous biramose limbs in which the exopodite, richly clothed with setae, 

 is specially apparent. The limbs of the abdomen are short rudiments, except 

 those of the sixth segment which, on the contrary, are well developed as the 

 long lateral divisions of the caudal fin, and are provided with setae. Later 



