66 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



body wall, which are known as gills or branchiae ; 



the presence of these has caused the name of 

 Branchiata to be given to this division of the Arthro- 

 poda. The greater number of the segments carry a 

 pair of appendages, and the great majority of these 

 are, in the lower forms, exactly similar in character 

 (Fig. 26, 5a). The metameres remain separate, and. are 



Fig. 26. Various Branohiopoda. 



1, Nelialia liipes (shell removed on one skle) ; 2, Estheria sp. ; Sa, 'dorsal : 3Z>, 

 ventral aspect of Lepidurus angassi ; 4, larva of Apus canciformis ; 5n, , adult 

 female of Branchipus stagnalis ; 5b, 5c, larvae ; 6, larva of Artemia salina. 



often very numerous ; in the higher forms they tend, 

 in a most remarkable manner, to be limited to about 

 twenty, and the dorsal parts of the hard exoskeleton 

 become fused in the anterior region (Fig. 27). 



In all, the mouth is moved so far back from the 

 anterior end of the body that two pairs of appendages 

 (antennae) lie in front of it. 



They are divisible into the Eiitomostraca, so 

 called from, the slight amount of fusion of the 



