98 The American Naturalist. [February, 



derstand the development of the higher organisms until this 

 problem is solved. Everybody is writing about the origin of 

 new organs, and we take lively pleasure in discussions about 

 acquired characteristics. But if we consider the circumstances 

 closely, we recognize that the loss of ancestral characteristics 

 almost equals in importance the acquisition of new character- 

 istics for the formation of new species. We assume that man 

 had fish like ancestors, and we strengthen ourselves in this be- 

 lief by the comparison so often made between the human em- 

 bryo, on the one side, and the adult fish on the other. But if 

 the comparison be impartial we are forced to admit that 

 nearly everything which is most characteristic of the fish is 

 conspicuously lacking in the human embryo. Taking the 

 embryo at the stage when the gill clefts have their maximum 

 development, we find the following relations : the body is not 

 straight but coiled up, and this coiling up is indispensable, in 

 order to bring about the proper distribution of the human 

 nerves, blood vessels, and so forth ; the gill clefts are closed ; 

 gills are wanting ; the digestive canal has no glands ; the epi- 

 dermis has no scales; the chorda dorsalis does not form a 

 large axis of the body, but is a minute string of cells. In 

 short, the Biogenetisches Grundgesetz (Recapitulation theory or 

 von Baer's law, according to Adam Sedgwick) is scarcely half 

 true. I have previously defended this conclusion at a meet- 

 ing of the American Society of Morphologists, in December, 

 1893, Subsequently, but independently, Adam Sedgwick has 

 reached a similar conclusion, see his paper " On the Law of 

 Development, etc:' (Quart. Jour. Micros. Sci., XXXVI, 35). 

 Were it not, as above implied, that the departures from the 

 fish type are in great excess, there would be no embryo at all, 

 and consequently no man, for the adult form is a conse- 

 quence of the embryonic. The embryo is the mechanical 

 cause of the adult body. How has the disappearance of the 

 ancestral fish characteristics been effected ? The question re- 

 mains unanswered. It will, perhaps, be replied " through dis- 

 use " or "through panmixia." But "disuse" is merely a 

 name, not an explanation of the phenomena. Panmixia is an 

 hypothesis erected on nothing. In fact, this hypothesis as- 



