CHAP. VII. DEVELOPMENTAL HISTORY. 47 



CHAPTEK VII. 



DEVELOPMENTAL HISTOKY OF PODOPHTHALMA. 



LET us first glance over the extant facts. 



Among the Stalk-eyed Crustacea (Podophthalma) 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. This is the case accord- 

 ing to Kathke 1 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 Planarise 

 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 



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

 of confirming. 



