THE FAIRY SHRIMPS (PHYLLOPODA) 665 



larva has no trace of trunk-somites; the first antennae are greatly 

 reduced and the labrum is very large. The trunk-somites and their 

 appendages become differentiated in regular order from before 

 backwards. The single median eye of the larva persists in adult 

 phyllopods. 



All Phyllopoda, except Artemia, live in small fresh- water pools, 

 especially those that are formed during spring rains and dry up 

 during the summer. In such situations they often occur in enormous 

 numbers. The writer once saw in Nebraska nearly half a bushel 

 of dead Apus bodies on the bottom of a shallow dried-up depression 

 about twenty feet in diameter. The eggs of most genera can re- 

 sist prolonged desiccation ; indeed it seems necessary for the develop- 

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

 immersed in water. Many eggs float when placed in water and 

 development takes place at the surface. The mud of dried pools 

 often contains large numbers of eggs that may be carried long 

 distances by winds, birds, or by other means. Many exotic species 

 have been reared from dried mud brought home by travelers. 



On account of the rapid evaporation of the pools in which they 

 live, phyllopods are able to withstand considerable changes in the 

 amount of mineral salts in the water. It is remarkable that, 

 though none of these crustaceans are marine, Artemia salina lives 

 in salt lakes and salt evaporating basins where the salinity far ex- 

 ceeds that of the ocean. One instance has been recorded where 

 the salts in solution were 271 grams per liter, and where the water 

 was of the color and consistency of beer. Artemia salina is subject 

 to marked form variations that are more or less correlated with 

 salinity, and both Kellogg and Artrom have observed that this 

 species tends to assume a reddish color as the water about it grows 

 denser. 



Phyllopods usually swim on their backs with the ventral surface 

 uppermost. Eubranchipus swims easily about when it is not rest- 

 ing on the bottom; Apus is a graceful swimmer but often creeps on 

 its ventral surface over the bottom and upon vegetation; Estheria 

 commonly burrows in the mud. Food is collected in the ventral 

 food-groove between the post-oral limbs whose gnathobases drive it 

 forward to the mouth. It consists of suspended organic debris, 



