254 BRITISH ENTOMOSTRACA. 



The natatory feet are very imperfectly developed ; their 

 function being supplied by two pairs of organs in form of 

 rami, placed on the anterior part of the body. The first pair 

 corresponds with the antenna in the perfect animal ; the 

 antenna itself being well developed, and the appendage 

 which projects from its posterior edge being enlarged into 

 this long ramus, constituting the chief part of the organ. 

 The second pair corresponds with the first pair of foot-jaws 

 in the adidt. These organs are large, consisting of several 

 articulations, the terminal one of which gives off several 

 long setae. By means of these rami the little creature 

 moves with ease by bounds, like the Daphnia. The 

 sucking-discs are not yet formed, their place being sup- 

 plied by a pair of large feet, broad at their base, and ter- 

 minating in a prehensile hook, by means of which the 

 animal can fix itself upon its prey. The organs imme- 

 diately folloAving these are only slightly developed, and 

 correspond with the third pair of foot-jaws, and the nata- 

 tory feet are little more than rudimentary. In this state 

 the young animal continues for about six days, when it 

 casts its shell. Three days after the first moult, it changes 

 its shell again ; and two days after that a third moult 

 takes place. By this time we find the rami have dis- 

 appeared, the natatory legs have become developed, and 

 the sucking-discs have assumed somewhat of their shape 

 and appearance. 



Two days after this the fourth change of shell takes 

 place, when the sucking-disc has become perfect. Six 

 days later, the fifth moult occurs, when the sexual organs 

 make their appearance ; and after the sixth change, which 

 takes place six days subsequently, or twenty-five days 

 from their being hatched, the animals commence to breed. 

 They have now, however, only attained half their full 

 growth, but gradually augment in size after successive 

 moults, which take place every six or seven days. 



An experiment conducted by Jurine, and fully detailed 

 by him, tends to prove that the Arguli do not, like some 

 of the Branchiopoda, become pregnant without the inter- 



