122 THE HISTORY OF CREATION, 
anatomy and ontogeny. Besides these, paleontology 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 common origin 
of all those animals which 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 ¢ 
