THE BR.VNCHIOPODA. 



249 



the head or the thorax, the segments of the latter being en- 

 tirely free, while the former is similar in shape to that of an 

 Insect, or Edrioplithalmous Crustacean, and carries two large 

 stalked eyes, two antennules (singularly modified in the 

 male), two antennae, a pair of mandibles, and two pairs of 

 maxilljie. 



In Estheria and Limnetis, the males are met with in full 

 proportion to, and may be even more numerous than, the 

 females. No males are known in Llmnadia gigas^ although 

 thousands have been examined, while, in X. ^tanleyana^ 

 more males than females have been found. In JBranchipus^ 

 males are fewer than females ; in Artetma, they occur only 

 at rare intervals. In Daphnia^ the males are few, and appear 



Fig. ^5.—Limnetis brachyurus (after Grnbe).— The upper left-hand figure is the 

 male, the other the female; one valve of the carapace in each case being removed. 

 A\ Antennules. A^, Antennae. A, Young larva. B, The same further advanced, 

 c, head ; o, eye ; d, carapace : &, bodv. A '. Antennae. J/, Mandible?, d', great 

 plate (labrum?) which covers the mouth. 



only at certain seasons of the year. But notwithstanding 

 the rarity or absence of the males in many of these genera, 

 reproduction proceeds with great rapidity. The ova are capa- 

 ble of development without fecundation ; and isolated females 



