PHENOMENA OF CONVERGENCE. 19 



the land crabs of the most different families con- 

 verge in their mode of life and physiology of 

 breathing. The transition from life in water to 

 life on land has commenced in the one and the 

 other species, here and there, and they meet in the 

 most different stages of capacity for life on land ; 

 no form is so far changed that its relation to some 

 definite family is not unquestionably evident. The 

 transition from a life in water to one on land has 

 transformed both feet and gills, but has not gone so 

 far as to show agreement or apparent homology. 

 In this case of convergence the mode of life has 

 remained the same as that in which the Eodents 

 resemble the Insectivora and the Cetacea the 

 Sirenia. They were judged differently without 

 principle or consistency. The agreements in the 

 Insectivora and the Kodents had always been 

 considered as accidental and purely external, 

 whereas the Cetacea and Sirenia were classed 

 together in one order as close relatives. 



We must here mention an attempt made by 

 Kolliker, 1 an eminent German scientific man, to 



1 Kolliker's Alcyonaricn in the Abhandlungen der SencJcen- 

 bergischen naturforschendew Gesellschaft, vii., viii. Published 

 separately under the title of Morphologie und Entwickelungs- 

 geschichte des Pennatulidenstammes nebst allgemeinen Betrach' 

 tungen zur Descendenzlehre. Frankfurt a.M., 1872. 



