INTRODUCTION. Vll 



biologist, whose theories were unfruitful, wrecked his wrath on the temple of 

 morphology and condemned its triune god to the consolation of his more credu- 

 lous colleagues; "Paleontology," he cried, "is mute, Comparative Anatomy 

 meaningless, and Embryology lies." 



But perhaps the fault was ours. We did not understand, because of igno- 

 rance and over confidence. It is not fifty years since the doctrine of evolution has 

 been generally recognized, and during the latter half of that period surprisingly 

 little persistent, or concerted work has been done on the larger problems of 

 phylogeny, and there is but little to justify the too common attitude that the pos- 

 sibilities of morphology are exhausted. Much disconnected fragmentary work 

 has been done, but how little is known about the evolution of any one organ or 

 system of organs; how very few animals, if indeed there are any, whose structure, 

 development, and paleontological record are known with even approximate 

 fullness or accuracy. What large class of animals is not separated from its next 

 of kin by a gap too wide to be bridged by any known forms ? Are these gaps due 

 merely to a hiatus in the available records, or in our knowledge of them, or are 

 they realities, representing periods of unusually rapid transformation due to 

 sudden changes in the methods, or conditions of growth? If the gaps between 

 the vertebrates and ostracoderms, and the ostracoderms and arachnids appear to 

 be wide ones, are they really any wider than those between the fishes and amphibia, 

 the reptiles and mammals, or the ccelenterates and arthropods? Are not the 

 evidences of genetic relationship of the same nature and value in one case as in 

 the other? Is not the paleontological record more precise and complete than we 

 have supposed ? Will not embryology be less enigmatic under a new interpreta- 

 tion ? If the arachnids are indeed the next of kin to the ostracoderms, and through 

 them to the vertebrates, is that after all so incredible ? With this gigantic column in 

 position, will not the remaining branches readily fall into their natural positions, 

 and the entire genealogical tree of the animal kingdom take on the convincing 

 symmetry and coherency of reality, of a living, growing organism that contains 

 the story of its own creation ? 



These are some of the problems bound up in the evolution of the vertebrates. 

 Clearly it is not merely a question of constructing a convenient and more or less 

 satisfactory genealogy of the animal kingdom. The whole philosophy of creative 

 evolution is involved in the answer. We must face these problems fairly, without 

 prejudice and without arrogance (surely the record of past achievements affords 

 no grounds for that attitude), and with a full recognition of their significance. 

 Facts are stubborn things that will not be ignored, that call out for recognition, 

 and for their proper location in a well ordered scheme, if not in one, then in some 

 other that is better. 



The problem is of the utmost importance to the biologist, for the answer 

 should determine the location of severallarge classes of animals, now completely 

 isolated; it will enable us to reconstruct the broad outlines of the genealogical 



