CONSTRUCTION OF THE PEDIGREE. 3 



or stage of the system (for example a class, or an order) 

 comprises a number of larger and stronger branches of the 

 pedigree ; eveiy narrower and lower category (for example 

 a genus, or a species) only a smaller and thinner group of 

 twigs. It is only when we thus view the natural system as 

 a pedigree that we perceive its true value. (Gen. Morph. ii. 

 Plate XVII. 397.) 



Since we hold fast this genealogical conception of the 

 Organic System, to which alone undoubtedly the future of 

 classificatory Zoology and Botany belongs, we should now 

 turn our attention to one of the most essential, but also one 

 of the most difficult, tasks of the " non-miraculous history of 

 creation," namely, to the actual construction of the Organic 

 Pedigree. Let us see how far we are already able to point 

 out all the different organic forms as the divergent descend- 

 ants of a single or of some few common original forms. 

 But how can we construct the actual pedigree of the 

 animal and vegetable group of forms from our knowledge 

 of them, at present so scanty and fragmentary ? The answer 

 to this question lies in what we have already remarked of 

 the parallelism of the three series of development — in the 

 important causal relation which connects the paleeontolo- 

 gical development of aU organic tribes with the embryological 

 development of individuals, and with the systematic de- 

 velopment of groups. 



In order to accomplish our task we shall first have to 

 direct our attention to palceontology, or the science of petri- 

 factions. For if the Theory of Descent is really true, if the 

 petrified remains of formerly living animals and plants 

 really proceed from* the extinct primaeval ancestors and 

 progenitors of the present organisms, then, without any- 



