250 THE DOCTRINE OF DESCENT. 
assumed, the value of the hypothesis is undiminished. 
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. 
Reptiles, 
\ ae 
ae 
Amniota. 
? Enaliosaurians. Amphibians. 
Careeas Al! 
| Amphioxus. 
UH ~— J 
[ Testacea. 
Se 
Primordial Vertebrata. 
Annulosa, 
As we have seen above, the most important indications 
of the pedigree of the species are contained in the evo- 
