134 THE THEORY OF EVOLUTION 



bosses, but, with these, reptilian-like teeth and a scaly 

 covering, since of an actual connection of our recent 

 reptilian orders with the Permian or later Stegocephali 

 nothing is known. Suppositions might be permissible 

 if the evolution for similarly varied animal groups 

 (as are the present Reptilia and those Stegocephali) 

 were demonstrated or at least were shown to be very 

 probable. 



Deperet chastises excellently this f method of 

 approximate estimation/ It consists therein that for 

 a genus of living or recent animals, whose genealogy it 

 is desired to ascertain, several other genera are selected 

 from the series of earlier geological periods which present 

 a certain analogy to the first in the structure of an 

 organ or in a small number of organs. With the aid 

 of these genera a series is arranged which, with regard 

 to the changes of the organs taken into consideration, 

 appears to fit in with natural evolution. For the Mam- 

 malia, for instance, there is taken as the touchstone, 

 sometimes the structure of the molars, sometimes the 

 canines, here the progressive regression of the side 

 toes, and there the graduated development of the 

 nasal bones, the horns, or antlers, while the rest of the 

 organization is almost entirely neglected. ' Further- 

 more, the chronological order of the appearance of the 

 fossil forms, which are serially arranged, does not cause 

 over-much embarrassment in these cases/ Thus have 

 Gaudry and Boule, in constructing the pedigree of the 

 Urcidse, between the Hyaenarctos out of the upper 

 Miocene and the first Bears (Ursus) out of the Pliocene, 



