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THE AM ERIC AX A .1 77 7,'. I /./>/' [Vol. XLIII 



gard to the matter of the light they might throw on the 

 nature and origin, and consequently upon the reality or 

 non-reality, of species. But the brief space remaining will 

 permit scarce a reference to them. Moreover, single in- 

 stances in biological fields can never prove general laws; 

 they can, at most, illustrate them and prepare our minds 

 for wider proof. 



Let us look for a moment, however, at the group of little 

 animals known as Hydra. Linnaeus, with his long spoon, 

 swallowed the whole genus at a gulp. He knew there 

 were differences, as his description shows, but he called 

 all by the one binomial, Hydra polypus. Soon, however, 

 zoologists became convinced that Linnaeus had been eating 

 too fast. There were more species than one. But how 

 many! Even yet unanimity has not been reached. Does 

 this constitute an argument for the unreality or for the 

 conventionality of species? In truth it does not. The 

 genus Hydra has never been fully investigated. Inter- 

 minable discussions of the undecipherable problems of 

 priority have not been lacking; some good observations, 

 and, much more to the point, some good culture experi- 

 ments have been made. But year-long, controlled and 

 pedigreed cultures are required, cultures successfully car- 

 ried through sexual as well as asexual phases. Had these 

 been carried out, as I trust they have been by the writer, 

 the truth of the conclusion would have been amply demon- 

 strated, that we have within the genus Hydra (whether 

 or not we shall ever be able to name them) a number of 

 highly autonomous aggregates of individuals, separated, 

 the one from the other, by a large number of minute but 

 highly constant differences. These groups are such, as 

 are commonly and appropriately called species, despite 

 the fact that the ordinary student with the collecting 

 bottle may be unable to distinguish them. To deny them 

 reality or treat their systematic segregation as a matter 

 of convention only is as inappropriate, because as untrue 

 to the facts, as to deny the reality of any and all distinc- 

 tions in nature. 



Certain of these differential characters are of special 



