308 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



segments appear for the first time (fig. 4a). The dorsal 

 and lateral spines of the abdominal segments are less 

 prominent, while two small ones appear on the rostrum. 



A third ecdysis occurs about the beginning of the 

 fourth week, and brings about still further changes (fig. 

 5). The flagella of the second antenna? are now long 

 and many jointed, and resemble those of the adult. The 

 plumose exopodites, no longer needed as swimming 

 organs, have almost completely lost the setae with which 

 they were fringed in their functional condition, and are 

 much reduced. The dorsal median line of the rostrum 

 is serrated, and the two spines on its front are well marked. 

 The abdominal swimmerets are fringed with setae, and 

 are used in swimming ; the telson (fig. 5a) has lost the 

 median spine on its now slightly convex posterior edge, 

 and a strong tooth appears on the outer edge of the 

 exopodites of the sixth abdominal segment. 



A fourth ecdysis occurs early in the fifth week, and 

 while the larva (fig. G) still swims actively, it spends much 

 time on the bottom and quickly appropriates any con- 

 venient hiding place. The chelae are almost invariably 

 rigidly extended in front when the animal swims. After 

 further ecdyses they become asymmetrical, as in the adult, 

 and the appendages of the first abdominal segment are 

 developed. The latter are at first of similar form in the 

 two sexes, but acquire sexual characters at a later stage. 



