T22 THE HISTOEY OP CREATION. 



anatomy and ontogeny. Besides these, palaeontology also 

 throws much valuable light upon the historical succession of 

 many of the groups. From numerous facts in comparative 

 anatomy, we may, in the first place, infer the coTnmon origin 

 of all those animals ivhich belong to one of the seven " types." 

 For in spite of all the variety in the external form developed 

 within each of these types, the essential relative position 

 of the parts of the body which determines the type, is 

 so constant, and agrees so completely in all the members 

 of every type, that on account of their relations of form 

 alone we are obliged to unite them, in the natural system, 

 into a single main group. But we must certainly conclude, 

 moreover, that this conjunction also has its expression in 

 the pedigree of the animal kingdom. For the true cause 

 of the intimate agreement in structure can only be the 

 actual blood relationship. Hence we may, without further 

 discussion, lay down the important proposition that all 

 animals belonging to one and the same circle or type must 

 be descended from one and the same original primary form. 

 In other words, the idea of the circle or type, as it is 

 employed in zoology since Bar and Cuvier's time to 

 designate the few principal main groups or " sub-kingdoms " 

 of the animal kingdoms, coincides with the idea of " tribe " 

 or " phylum," as employed by the Theory of Descent. 



If, then, we can trace all the varieties of animal forms to 

 these seven fundamental forms, the following question next 

 presents itself to us as a second phylogenetic problem — 

 Where do these seven animal tribes come from ? Are they 

 seven original primary forms of an entirely independent 

 origin, or are they also distantly related by blood to one 

 another ? 



