ZOOLOGY SINCE DARWIN. 479 



Finally, however, it affected both in the same way, and there are but 

 few examples in the history of the development of the human mind 

 that show such a revolution in the elementary principles of a science 

 as the theory of natural selection has affected in the above-mentioned 

 studies. Instead of being contented with mere description and lucid 

 arrangement, there was undertaken the higher task of determining the 

 causal relations of forms ; ant-like descriptive industry had to associate 

 itself with the comparative method; the eye had to seek assistance 

 from the imagination. 



As the first and most urgent task, appeared the changing of the 

 classification hitherto followed according to the lines laid down by 

 Linnreus and Cuvier into one which should correspond with the his- 

 tory of the descent of living beings. The fiery spirit of E. Haeckel 

 tried to accomplish this, when, in his brilliantly devised system of the 

 organic natural sciences, the General Morphology of Organisms, 1 he 

 attempted to determine the primitive stocks. However rash this may 

 have been, considering the state of zoology at that time, it rendered 

 an inestimable service by giving the first impulse toward that great 

 development of animal morphology that has taken place during the 

 last decade. Modern morphology first dates from that time, when, as 

 formerly stood Schiller and Goethe, Haeckel, and Gegenbaur worked 

 side by side. Since that time it has become so essential a part of 

 scientific zoology that the text-books of to-day are only too much given 

 up to comparative morphology. 



The "fundamental law of biogeny" formulated by Haeckel, namely, 

 that ontogeny (the development of the individual) is a short recapitu- 

 lation of phylogeny (the development of the stock), soon dominated all 

 branches of zoology, controlling comparative anatomy, embryology, and 

 paleontology. Since the ancestral stages traversed by an animal are 

 repeated in a more or less recognizable manner in the transitory forms 

 assumed during the development of each individual, so embryology 

 came in the post-Darwinian times to be considered as a necessary 

 study. To this is chiefly due the enormous increase in zoological pub- 

 lications, which, during the period from 1845 to 1860, amounted to a 

 yearly average of 2,900, but in that from 1860 to 1880, increased to 

 about 5,100 per year. 2 



Simultaneously with this increase in literary production, there 

 occurred an improvement in the technical methods of research. Innu- 

 merable staining methods enabled the investigator to study more 

 accurately the structure of the cell, to separate its nucleus from its 

 plasma, as also to define the constituent portions of each according 

 to their various susceptibilities to staining. 



'E. Haeckel, Generelle Morphologie der Organismen, Berlin, 1866. 



2 As a basis for this calculation, I have used J. V. Cams and W. Englemanrj, 

 "Bibliotheca zoologica" Leipzig, 1861, andO. Taschenberg, " Bibliotheca zoologica," 

 II, Leipzig, 1887-1896. 



