CRUSTACEA OF FRESH WATERS 161 



sea, and some Anostraca in salt lakes and brine 

 pools. 



The larger Branchiopoda (Anostraca, Notostraca, 

 and Conchostraca) are generally found in small, 

 shallow ponds which are liable to be dried up 

 in summer. The " Fairy Shrimp " (Chirocephalus 

 diaphanus; see Fig. 10, p. 35) has been found in 

 swarms in the water standing in deep cart-ruts in 

 a country lane in England, and Apus sometimes 

 appears suddenly in rain-water puddles of a few 

 square yards in area, which dry up after a few weeks 

 of hot weather. The eggs of these animals, when 

 dried in the mud, may remain dormant for long 

 periods, and many species have been hatched out 

 from samples of dried mud brought by travellers 

 from distant countries. In such a sample from the 

 Pool of Gihon at Jerusalem, it is recorded that the 

 eggs of Estheria (see Fig. n, p. 36) were found to 

 be capable of hatching after being kept dry for nine 

 years. In some species it is said that the eggs will 

 not develop unless they have been first dried, but 

 this is not the case with Chirocephalus. In favour- 

 able conditions development takes place very rapidly. 

 Messrs. Spencer and Hall, in describing the Branchi- 

 opoda of Central Australia, say : " Certainly not more 

 than two weeks after a fall of rain, and probably 

 only a few days, numberless specimens of Apus, 

 measuring in all about 2| to 3 inches in length, were 

 swimming about ; and, as not a single one was to be 

 ii 



