306 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



regular order upon it. The posterior edge of the telson 

 (fig. la) at this stage is rather deeply cleft. The 

 abdomen is at once extended, the exopodites of the third 

 pair of maxillipedes and of the five pairs of walking legs 

 assume their function as swimming organs, and the tiny 

 animal begins its free swimming life in what is known as 

 the My sis stage (fig. 2). The carapace has a simple 

 frontal rostrum and a minute lateral spine on either side, 

 close to the compound eye. The third to the sixth seg- 

 ments inclusive of the abdomen have dorsal and lateral 

 spines, and there is a single minute median spine on the 

 posterior edge of the telson (fig. 2a), which is now T much 

 less deeply cleft and fringed with seta?. The first antenna? 

 are unjointed, the second are biramose. The penulti- 

 mate and terminal joints of the three anterior pairs of 

 walking legs form pincer-like organs, as in the adult. 

 Thus constituted, the larva swims actively, with the 

 plumose exopodites of the walking legs and third maxilli- 

 pedes projecting laterally like oars, and the abdomen 

 rather strongly flexed beneath the thorax. This stage 

 persists until about the seventh day, when the first ecdysis 

 takes place, and several new features in the structure of 

 the larva appear (fig. 3). The second, third, fourth and 

 fifth segments of the abdomen now T bear rudimentary 

 swimmerets. The principal flagella of the first antenna* 

 are segmented and rudimentary accessory flagella appear. 

 Little change is noticeable in the telson (fig. 8a). 



A second ecdysis occurs about the fourteenth day, 

 and introduces the third larval stage, which presents 

 additional structural features of importance (fig. 4). The 

 first pair of walking legs are now proportionately larger 

 than their successors, and foreshadow the great chela? of 

 the adult. The abdominal swimmerets are more con- 

 spicuous, and the appendages of the sixth abdominal 



