IX THE HISTORY AND SCOPE OF ZOOLOGY 343 



chemical laws of the universe, and it was recognised 

 that the ultimate explanation of that limitation is to 

 be found only in the constitution of matter itself. 



The first naturalist to put into practical form the 

 consequences of the new theory, in so far as it affected 

 zoological classification, was Ernst Haeckel of Jena 

 (6. 1834) who in 1866, seven years after the publica- 

 tion of Darwin's Origin of Species, published his sug- 

 gestive Generelle Morphologic. Haeckel introduced 

 into classification a number of terms intended to indi- 

 cate the branchings of a genealogical tree. The whole 

 '^ system " or scheme of classification was termed a 

 genealogical tree [Stammbaum) ; the main branches 

 were termed '' phyla," their branchings " sub-phyla" ; 

 the great branches of the sub-phyla were termed 

 " cladi," and the " cladi " divided into '' classes," these 

 into sub-classes, these into legions, legions into orders, 

 orders into sub-orders, sub-orders into tribes, tribes 

 into families, families into genera, genera into species. 

 Additional branchings could be indicated by similar 

 terms where necessary. There was no attempt in 

 Haeckel's use of these terms to make them exactly or 

 more than approximately equal in significance ; such 

 attempts were clearly futile and unimportant where 

 the purpose was the exhibition of lines of descent, and 

 where no natural equality of groups was to be expected 

 ex hypothesi. Haeckel's classification of 1866 was 

 only a first attempt. In the edition of the NaturUche 

 Schopfungsgeschichtc published in 1868, he made a 

 great advance in his genealogical classification, since 

 he now introduced the results of the extraordinary 



