32 CRUSTACEA—BRANCHIOPODA CHAP. 
all Apodidae, while the males of several species of Zimnadia 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 Apus 
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 11 
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 Rouen. 
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 (eg. of Chirocephalus diaphanus 
and Branchipus 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 stagnant 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 Branchipus, 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 
egos, 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 
