CHAP. IX. DEVELOPMENT OF BHANCHIOPODA. 83 



CHAPTEE IX. 



DEVELOPMENTAL HISTOKY OF ENTOMOSTEACA, CIRRI- 

 PEDES, AND RHIZOCEPHALA. 



THE section of the Branchiopoda includes two groups 

 differing even in their development, the Phyllopoda 

 and the Cladocera. The latter minute animals, pro- 

 vided with six pairs of foliaceous feet, which chiefly 

 belong to the fresh waters, and are diffused under 

 similar forms over the whole world, quit the egg witli 

 their full number of limbs. The Phyllopoda, on the 

 contrary, in which the number of feet varies between 

 10 and 60 pairs, and some of which certainly live in 

 the saturated lie of salterns and natron-lakes, but of 

 which only one rather divergent genus (Nebdlia) is 

 found in the sea, 1 have to undergo a metamorphosis. 

 Mecznikow has recently observed the development of 

 Nebalia, and concludes from his observations "that 

 Nebalia, during its embryonal life, passes through the 



1 If the Phyllopoda may be regarded as the nearest allies of the 

 Trilobites, they would furnish, with Lepidosteus and Polypterus, 

 Lepidosiren and' Protopterus, a further example of the preservation 

 in fresh waters of forms long since extinguished in the sea. The 

 occurrence of the Artemias in supersaline water would at the same time 

 show that they do not escape destruction by means of the fresh water, 

 but iu consequence of the less amount of competition in it. 



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