A PROBLEM IN EVOLUTION 



423 



the vertebrates, for in that case both would be derived from the same 

 stock. 



Here then, contrary to all our preconceived ideas, Avas a new solu- 

 tion of an old and very important problem, probably the most important 

 one before the morphologist since Darwin's time. It was evident that 

 this solution of it, if sustained, would lead to more radical changes in 

 the classification of the animal kingdom than any that have been made 

 since the time of Cuvier and Lamarck. Stated concisely, it was as 

 follows: At some time toward the close of the Cambrian period the 

 sea-scorpions probably gave rise to the ostracoderms, and the latter, 



,pa.ey. Olfactory. 

 Coord 

 Visual. 



ol.o. 



s 



\ 



Ostracodenfc * ^•^°< 



Fig. 2. Semi-diagrammatic Figures of a Sea Scorpion (Eurypterid) and an 

 Ostracoderm (Bothriolepis) , showing the sequence in the location of the important 

 functions, and the subdivisions of the body corresponding to the subdivisions of the 

 head and brain in the higher vertebrates. 



during the Silurian, to the fishes, or first true vertebrates (Fig. 3). 

 This was an entirely new interpretation in phylogeny, but it was not 

 inherently improbable, or contrary to any established facts ; indeed, the 

 first demands of the theory were in full accord with the known facts 

 of anatomy, embryology and paleontology. Let us state it again in 

 this way: In their fundamental structure, living arachnids resemble 



