3 2 CRUSTACEA — BRANCHIOPODA chap. 



all Apodidae, while the males of several species of Limnadia are 

 still unknown, although the females are sometimes exceedingly 

 common. In Artemia, generations in which the males are about 

 as numerous as the females seem to alternate fairly quickly with 

 others which contain only parthenogenetic females ; in A2nis 

 males are rarely abundant, and often absent for long periods ; 

 during five consecutive years von Siebold failed to discover a 

 male in a locality in Bavaria, though he examined many thousands 

 of individuals ; near Breslau he found on one occasion about 1 1 

 per cent of males (114 in 1026), but in a subsequent year he 

 found less than 1 per cent ; the greatest recorded percentage of 

 males is that observed by Lubbock in 1863, when he found 33 

 males among 72 individuals taken near Ilouen. 



The eggs of most genera can resist prolonged periods of 

 desiccation, and indeed it seems necessary for the development 

 of many species that the eggs should be first dried and afterwards 

 placed in water. Many eggs {e.g. of Ghirocephalus Aia])lhanus 

 and Branclii'pus stagnalis) float when placed in water after desic- 

 cation, the development taking place at the surface of the 

 water. 



Habitat. — All the Phyllopoda, except Artemia, are confined 

 to stagna.nt shallow waters, especially to such ponds as are formed 

 during spring rains, and dry up during the summer. In waters 

 of this kind the species of Branchi^ms, Apus, etc., develop rapidly, 

 and produce great numbers of eggs, which are left in the dried 

 mud at the bottom after evaporation of the water, where they 

 remain quiescent until a fresh rainy season. The mud from the 

 beds of such temporary pools often contains large numbers of 

 eggs, which may be carried by wind, on the legs of birds, and by 

 other means, to considerable distances. Many exotic species have 

 been made known to European naturalists by their power of 

 hatching out when mud brought home by travellers is placed in 

 water. The water of stagnant pools quickly dissolves a certain 

 quantity of solid matter from the soil, and often receives dissolved 

 solids through surface drainage from the neighbouring land ; such 

 salts may remain as the water evaporates, so that the water which 

 remains after evaporation has proceeded for some time may be 

 very sensibly denser than that in which the Branchiopods were 

 hatched ; these creatures must therefore be able to endure a con- 

 siderable increase in the salinity of the surrounding waters during 



