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THE AMERICAN NATURALIST 



[Vol. XLII 



aside from cases of this kind, all phyla that might be rep- 

 resented by fossils are, as a matter of fact, so represented ; 

 and the remarkable feature of this representation is that it 

 does not show a convergence toward a common stock, 

 bnt the phyla as such were as distinct in these early times 

 as they are to-day. This state of affairs, which at first 

 sight seems contrary to the evolutionary idea, is due in 

 all probability to a universal destruction by extensive 

 rock metamorphosis of the earliest of animal remains, 

 and we are therefore probably correct in concluding that 

 fossils at best give us only the later chapters in the evo- 

 lution of the animal kingdom. Within a phylum the main 

 lines of descent can sometimes be clearly discerned, but 

 between phyla there are no absolutely certain connections, 

 nor is there as a matter of fact a single completely ex- 

 tinct phylum known. These facts lead us to see that for 

 an immensely long period the main divisions of the animal 

 kingdom have been as they are at present and that the 

 genetic connections of the phyla, which would be discern- 

 ible with certainty only through their fossil remains, are, 

 in consequence of the absence of these, probably abso- 

 lutely and irrecoverably lost. Even the important sug- 

 gestions that embryology has yielded as to the phylogen- 

 etic relations of the chief animal groups must remain 

 forever hypotheses because of this irreparable blotting 

 out of past records. 



Although the systematic zoologist may look upon the 

 animal kingdom as composed of imperfectly definable 

 aggregates of individuals whose relations in the remote 

 past are irretrievably lost but whose numbers are such 

 as to occupy his labors for many years to come, his arrival 

 at this conception has been over a course that has brought 

 to view such a multitude of new prospects that the real 

 extent of zoology is only now beginning to be dimly seen. 

 These more recently acquired territories, which are now 

 being cultivated with a vigor no less than that bestowed 

 in past times almost exclusively on systematic zoology, 

 must now be looked into. It is somewhat difficult for us 



