Chap. VII. DEVELOPMENTAL HISTORY. 47 



CHAPTER YII. 



DEVELOPMENTAL HISTOEY OF PODOPHTHALMÄ. 



Let us first glance over the extant facts. 



Among tlie Stalk-eyed Crustacea (Podo^hthalma) we 

 know only a very few species which quit the egg in the 

 form of their parents," with the full number of well- 

 jointed appendages to the body. Tliis is the case accord- 

 ing to Eathke^ in the European fresh-water Crayfish, 

 and according to Westwood in a West Indian Land 

 Crab (Gecarcinus). Both exceptions therefore belong 

 to the small number of Stalk-eyed Crustacea which live 

 in fresh water or on the land, as indeed in many other 

 cases fresh-water and terrestrial animals undergo no 

 transformations, whilst their allies in the sea have a 

 metamorphosis to undergo. I may refer to the Earth- 

 worms and Leeches among the Annelida, which chiefly 

 belong to the land and to fresh water, — to the Flanaride 

 of the fresh waters and the Tetrastemma of the sparingly 

 saline Baltic among the Turbellaria,-^to the Pulmonate 

 Gasteropoda, and to the Branchiferous Gasteropoda of 

 the fresh waters, the young of which (according to 



^ Authorities are cited only for facts which I have had no opportunity 

 of confirming. 



