250 THE DOCTRINE OF DESCENT. 



vision assumed, the value of the hypothesis is undimin- 

 ished. It was the road to truth. 



In our science Haeckel has made the most extensive 

 use of the right of devising hypothetical pedigrees as 

 landmarks for research. It matters nothing that he has 

 repeatedly been obliged to correct himself, or that others 

 have frequently corrected him; the influence of these 

 pedigrees on the progress of the zoology of Descent is 

 manifest to all who survey the field of science, not to 

 mention that in the last ten years a series of researches 

 have conclusively fixed their results in good pedigrees. 

 As we propose to give merely an introduction to the 

 doctrine of Descent, we shall content ourselves with 

 showing how the system or the pedigree is constituted 

 in its application to the single group of the Vertebrata. 



Mammals. 



Birds. 



I 



Reptiles. 



Amniota. 

 ? Enaliosaurians. 



Primordial Vertebrata. 



I 



Annulosa. 



As we have seen above, the most important indica- 

 tions of the pedigree of the species are contained in the 



