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THE AMERICAN NATURALIST [Vol. XL VI 



that discontinuous mutations or saltations may be mere 

 ripples on the surface of these tides. 



Whatever the truth as to this thought, by a strange 

 paradox it is certain that some stationary characters, 

 some apparently dead things in the eyes of the zool- 

 ogist and botanist, become movable and alive in the eyes 

 of the paleontologist. Thus a paleontologist comes be- 

 fore the Harvey Society of Physiologists and Physicians 

 with the conviction that his vision is of a different angle 

 from that of the experimentalist, and that by the tri- 

 angulation of experiment, of anatomy and of paleontol- 

 ogy the truth may at least be more nearly approached. 



Is there more evidence of discontinuity and of law- 

 lessness, or of continuity and of law, in the origin of new 

 characters? Perhaps no more appropriate question 

 could be chosen as the subject of a lecture in memory of 

 William Harvey, the author of the doctrine of epi- 

 genesis, for the essence of this doctrine is that of 

 " successive differentiation of a relatively homogeneous 

 rudiment into the parts and structures which are char- 

 acteristic of the adult." Paleontology is at one with 

 embryology in the belief that differentiation is in the 

 main gradual and continuous. 



Yet to our question the answer prevailing among ex- 

 perimentalists and Mendelians at the present time is that 

 there is little evidence either for continuity or for law; 

 this despite the fact that a large part of the evidence for 

 discontinuity in the origin of characters is most un- 

 sound. In fact, our first purpose in this Harvey Lecture 

 is to show how surprisingly unsound this evidence is 

 when we consider that discontinuity has become prac- 

 tically a dogma among a very large number of zoologists 

 and botanists. It is true that the evidence for discon- 

 tinuity in the heredity of characters is as convincing as 

 that for discontinuity in the genesis of characters is de- 

 batable. Our second purpose in this Harvey Lecture is 

 to show that the evidence for continuity in the genesis 

 of certain characters in man and other mammals is very 



