1896. ZOOLOGY SINCE DARWIN. 367 



animal system is ignorant of the deep correlation existing between 

 seemingly immaterial outward characters and important points in 

 internal organisation, so that artificial systems built on the former 

 alone nevertheless result in a grouping quite corresponding to natural 

 relationships ? 



The necessity of a change in this direction was, of course, recog- 

 nised. Soon after its foundation in 1890, the German Zoological 

 Society resolved upon the compilation of a gigantic systematic 

 work, comprising all hitherto known species of animals, 5 and caused 

 a new edition to be printed of Linnaeus' " Systema Naturae." ^ 

 These are eloquent signs of the general need of deeper systematic 

 work. 



Yet it must not be overlooked that even the best descriptions of 

 species to-day are pure abstractions, which comprise in one united 

 individually coloured picture the results of research on a more or less 

 large number of individuals. Through such syntheses as these one 

 arrives at ideal species to which no one individual ever quite corres- 

 ponds, and which do indeed satisfy the first-felt requirement, viz., 

 comprehensibility, but which can never supply the material that we 

 need for the scientific extension of the theory of descent. For that 

 one would really want exact descriptions (divested as much as possible 

 of the subjective) of countless single objects. It would be necessary 

 to portray exactly the united examples of many generations with all 

 individual traits, especially in those species to which great variability 

 is ascribed. If the crossing of individuals could be carried on under 

 varying external conditions, it would be possible to distinguish 

 between constantly-inherited and variable characters. In the domain 

 of botany an attempt of this sort has been made, namely, in Nageli's 

 *' Researches on Hieracise,"^ in which this quick-witted thinker insists 

 upon the importance of a sharp division between uniformity and 

 constancy on the one hand, and between multiformity and variability 

 on the other. In the animal world such experiments as these are 

 very much more difficult, but certainly not impossible, and yet hardly 

 any have been undertaken.^ In this province there lies open to the 

 systematists of the future a field of work as large as it is fertile. 



Systematics, therefore, which, in the descriptive period before 



5 The publication of this is happily ensured already, and competent workers have 

 been secured for most of the animal groups. It will appear under the title, " Das 

 Tierreich : Eine Zusammenstellung und Kennzeichnung der rezenten Tierformen," 

 published by R. Friedlander und Sohn, Berlin. (See Natural Science, vol. viii., 

 p. 305, May, 1896.) 



6 Caroli Linnaei, "Systema Naturae, regnum animale.' Editio decima, 1758. 

 Cura societatis zoologicae germanicse iterum edita. Berolini, 1894. 



7 C. v. Nageli, " Mechanisch-physiologische Theorie der Abstammungslehre," 

 pp, 239 et seq. Munich and Leipzig, 1894. 



8 Even for the most elementary of the problems here named, viz., the one 

 concerning the degree of variability of animal species in nature, very little material 

 has hitherto been collected. Cf. A. R. Wallace, " Darwinism." 



