Chap. IX. DEVELOPMENT OF BKANCHIOPODA. 83 



CHAPTEK IX. 



DEVELOPMENTAL HISTORY OF ENTOMOSTEACA, CIERI- 

 PEDES, AND EHIZOCEPHALA. 



The section of the Brancliiopoda 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 with 

 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 (Nehalia) is 

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

 Mecznikow has recently observed the development of 

 Nehalia, and concludes from his observations "that 

 Nehalia, during its embryonal life, passes through the 



^ If the Phyllopoda may be regarded as tlie nearest allies of the 

 Trilobites, they would furnish, with Lepidosteus and Folypterus, 

 Lepidosiren and Frotopterus, a further example of the preservation 

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

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

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

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



G 2 



