490 ZOOLOGY SINCE DARWIN. 



artificial systems built upon those alone are found to correspond to the 

 grouping according' to natural relationships'? 



It is well known that a change in this policy is required. So the 

 Deutsche Zoologische Gesellschaft resolved, soon after its successful 

 establishment in 1890, to publish an immense, systematic work 1 embrac- 

 ing all the forms of animals known up to this time, and also undertook 

 a new edition of the Systema ISTaturre of Linnaeus. 2 These are eloquent 

 signs of the necessity for profound systematic work. 



Yet it should not be overlooked that the best modern descriptions of 

 species are pure abstractions that seek to embrace in a single specially 

 colored picture the result of the researches made upon a greater or less 

 number of individuals. By a synthesis of this sort we form ideas of 

 species to which no single individual ever exactly corresponds, and 

 which, while they suffice indeed for the prime necessity of lucidity, can 

 never give the materials needed for the scientific construction of the 

 theory of descent. For that purpose there would be required descrip- 

 tions, as exact and bare as possible, of numerous single objects. It 

 would be necessary to exactly portray the collective examples of several 

 generations with all their individual traits, especially in the case of such 

 species as were considered variable. If the race then encountered dif- 

 ferent external conditions, it would in this way be possible to separate 

 the constant, inherited characters from the variable ones. In the botan- 

 ical field there exists, in Nageli's work on the Hieraeese, an investiga- 

 tion of this kind which has given to that acute thinker an opportunity 

 to remark on the importance of a sharp distinction between uniformity 

 and constancy, as well as between multiformity and variation. 3 In the 

 animal kingdom, while such experiments are much more difficult, they 

 are certainly not impossible, and yet they are entirely unknown. 4 In 

 this direction there is open to the systematists of the future a great and 

 remunerative field for work. 



So we find that systematic zoology, which in the " descriptive" age 

 before Darwin, confined itself to short differential diagnoses and inven- 

 tories arranged for clearness only, but afterwards took upon itself the 

 office of an ancestral tree, defining true blood relationships, is to become, 

 in the next rjeriod of our science, quite indispensable to the experi- 

 mental method. 



'The publication of this is fortunately already secured and for most groups of the 

 animal kingdom competent editors have been obtained. It will appear under the 

 title: Das Tierreich. Eine Zusammenstellung und Kennzeichnung der rezenten 

 Tierformen. To be published by E. Friedlander und Sohn in Berlin. 



s Caroli Linnaji Systema naturae, regrium animale. Editio decima, 1758. Cura 

 societatis zoological germanicae iterum edita. Berolini, 1894. 



:; C. v. Niigeli, Mechanisch-physiologische Theorie der Abstammungslehre, page 

 239 ff. Miinchen und Leipzig, 1894. 



4 Even for the most elementary of the questions here considered, that of the degree 

 of variability of animal species in a state of nature, there has been up to the present 

 time but little material collected. Compare A. E. Wallace, Darwinism, authorized 

 translation into German by D. Brauns, Braunschweig, 1891. 



