xvi THE HISTORY OF ZOOLOGY 689 



A. R. Wallace's Geographical Distribution of Animals (1876), each 

 the first complete treatise on the subject in question. The zoo- 

 geographical regions adopted by Wallace were originally proposed 

 by P. L. Sclater in 1857. Similar landmarks for Zoology as a 

 whole are Huxley's Anatomy of Vertebrated Animals (1871) and 

 Anatomy of Invertebrated Animals (1877), Carl Gegenbaur's Ele- 

 mentsof Comparative Anatomy (English edition, 1878), Claus's Text- 

 Book of Zoology, (1st English edition, 1884-5), Ray Lankester's 

 Notes on Embryology and Classification (1877), and the same author's 

 articles in the Encyclopaedia Britannica (9th edition). Both Glaus 

 and Gegenbaur retain Vermes as a primary division ; Lankester 

 was the first to split up that unnatural assemblage into distinct 

 phyla, and to include Balanoglossus and the Tunicata among 

 Vertebrates, and Xiphosura and Eurypterida among Arachnida. 

 He also associated Rotifers and Chsetopods with Arthropoda, and 

 placed Hirudinea among the Platyhelminthes. A later develop- 

 ment of the same author's views on morphology and classification 

 is embodied in his Treatise on Zoology, of which six volumes have 

 now been published (see Appendix, 42). Of inestimable value in 

 the advancement of the embryology of Vertebrates is the com- 

 prehensive Handbuch (1901-1906) of O. Hertwig, with sections 

 by various other embryologists. 



The student who is interested in the permutations and com- 

 binations of modern classification may be referred to the works just 

 quoted as well as to the numerous text-books published of late 

 years. The most important point to notice in this connection is 

 the breaking down of the sharp boundaries between the four 

 Cuvierian Branches and a return to something like the conception 

 of unity of type, expressed, however, not as a linear series, but as a 

 branch-work with the most complex and often puzzling inter- 

 relations. 



Among the numerous recent contributions to philosophical 

 Zoology it must suffice to mention the works on heredity and 

 kindred subjects of August Weismann, the most prominent 

 member of the ultra-Darwinian school, who deny use-inheritance 

 and rely upon natural selection as the main, if not the sole, factor 

 in evolution. The opposite view, which accepts the truth of use- 

 inheritance, is mainly supported by the American school of Neo- 

 Lamarckians. Weismann has also resuscitated the theory of 

 pre-formation under a modern form. He considers that the 

 various parts of the adult organism are represented in the 

 chromatin (germ-plasm) of the sex-cells by ultra-microscopic 

 particles or determinants. These and allied topics are comprehen- 

 sively treated from a different standpoint by O. Hertwig in his 

 Allgemeine Biologie (1909). 



In a brief sketch like the present it is impossible to do more 

 than refer, in general terms and without mention of names, to the 



