DISTINCTIVE CHARACTERISTICS. 35 



often suffice to determine the order. A whole toe 

 \vill give a complete idea of the mode of life and of 

 the appearance of the primeval or still living 

 animal. In order, therefore, to obtain an insight 

 into the relationship and social position of a 

 mammal form, we must first of all become ac- 

 quainted with the foot of the vertebrate in its 

 simplest accessible form, and then examine the 

 different variations of the mammal foot under the 

 supposition of direct transformation. This study 

 was undertaken for the first time with perspicuity 

 and success by Gegenbauer ; and thus later modifi 

 cations which became specially necessary, owing 

 to the primeval form of fin of the Australian 

 Ceratodus could perfectly well be explained in 

 connection with Gegenbauer's conclusions both by 

 himself and others. 



The simplest form of hand and foot is met with 

 in the four-fingered and five-toed Amphibians and 

 various reptiles, e.g. the tortoises. Among the former 

 the rudiments of a sixth, sometimes even of a seventh, 

 toe are met with ; but with the exception of these 

 few indications, and the sixth finger of some 

 amphibian-like primeval animals, there are no 

 fossils relating to the early history of hand and 

 foot, or their transformation from the fish's fin. 



