REIGHARD ON THE BIOLOGICAL SCIENCES. 25 



miiuity of living being^s, received flesh and blood and demanded to be 

 included with the existin*,^ fauna and flora in a single great genealogical 

 tree, representing Ihr history of lifV on our earth." 



Darwin's b<)(>k brought essentially two contributions. In the lirst 

 place it brought a nuiss of tivdenve in proof of the projtosition that 

 aninuils are related to one another by descent. The idea of a jirocess of 

 evolution is very old and Osborn has recently traced its history from the 

 early (Ireeks to the time of Darwin. Darwin did not originate the idea, 

 he established it by a mass of evidence and it has been ever since 

 accepted. 



In the second jilace Darwin contributed the theory of the origin of 

 species by natural selection. This theory is so well known that it need 

 not be restated here, but it may jterhaps be pointed out that the theory 

 does not attempt to account for the origin of the variations upon which 

 it depends. It is a fact that these variations occur and Darwin's 

 theor* bases itself upon this fact. He spoke of such variations as 

 fortuitous. Aside from certain correlations, variations seemed to 

 Darwin to occur by chance, though he did not exclude the possibility of 

 their being later found to be subject to law. 



The idea that the multitude of animal forms had thus originated by 

 a process of evolution, and that this process was governed by a simple 

 law, affected the whole subsequent course of zoology. 



Zoologists soon came to accept not only evolution as a process, but 

 natural selection as at least the chief explanation of the process. The 

 zoologists following Darwin made but little attempt to study the 

 variations upon which the theory of natural selection based itself, or to 

 determine the range of variations or their causes. Having decided 

 that animals were related to one another, and having fixed the law 

 governing the origin of the relationship, zoologists began to turn their 

 attention to a study of the degree of relationship. A mania seems to 

 have become prevalent for the construction of a genealogical tree of the 

 entire animal kingdom. The ultimate aim of zoologists ten years ago, 

 or even five years ago was animal genealogy, and such is still the aim 

 of many working zoologists. Paleontology, comparative anatomy and 

 embryology were believed to furnish the means for unraveling animal 

 genealogies. 



All three of these lines of research have been pursued (from the 

 phylogenetic standpoint) with great enthusiasm since 1859, and they are 

 still being pursued; the results have, however, fallen far short of meet- 

 ing anticipations. From the paleontological side it was evident from 

 the first that many animals had left no recognizable fossil remains. 

 In other cases the lemains were so imperfect, so difficult of access and 

 so few that nothing like a complete series could be hoped for. Paleon- 

 tology has accomplished a great deal. Where it is available, it is without 

 doubt the safest guide, perhaps the only safe guide in phylogenetic 

 speculation. On the other hand it has not. and in the nature of its 

 materials cannot lead to a realization of the zoologist's dream of a 

 j)hylogeuetic millenium. 



(/om]>arative anatomy has been to a considerable extent neglected 

 during the past thirty years. Among the invertebrates, where the 

 research could be carried on by the rapid methods of modern microscopic 

 4 



