B78 Br. W. Kiikenthal on the Origin and 



mammalian stem, wliich still persists with least alteration in 

 the monotremes, and that certain of their orders have acquired 

 the placenta independently of one another *. The marsu- 

 pials form a branch which runs parallel to the placental 

 mammals, and likewise originated from the main stem. The 

 resemblances witliin the individual orders of the two sub- 

 classes are merely instances of convergence. 



It is not my intention to follow out the development of the 

 mammalian phylum in detail, enticing though it would be 

 to show how the hypotheses derived from tlic study of compa- 

 rative anatomy and embryology are supported by the palgeon- 

 tological discoveries which are multiplied from year to year. 

 It was rather my desire to bring forward certain problems 

 which are connected with the investigation of the mammalian 

 phylum, and to expose the methods by whicli work is novv-a- 

 days carried on. 



Far from regarding the erection of a sort of picture-gallery 

 of ancestors as the goal to which our science should aspire, 

 we rather seek to obtain a clue to the complicated causes 

 whicli have brought about the immense variety of animal 

 forms. We would discover the laws which the organic world 

 obeys. 



At the same time, however, I would wish to combat the 

 fundamental error of believing the problem of life to be 

 solved, if we should succeed in recognizing the mechanical 

 laws which have been active in the develoj)ment and moditi- 

 cation of organic bodies. The knowledge of the vital pro- 

 cesses themselves is not in the least advanced thereby ; with 

 the same degree of justice we could, to use Bunge's simile, 

 regard the movement of the leaves and twigs on the tree, 

 which are tossed by the storm, as manifestations of life. 

 What we are able to perceive is nothing else than the way 

 in which living matter reacts upon forces coming from 

 without. This task, which has been attacked in its full 

 e:xtent by the physiology of to-day, has recently been claimed 

 by a number of, for the most part, junior investigators as the 

 sole object to which biological science has to devote itself. 

 While claiming to have discovered an absolutely new method 

 of biological investigation, tliey believe that this mecluuiico- 

 etiological method is the only way wliich we dare follow for 

 the solution of biological questions, and that the " morpho- 

 logico-historical " method, based upon the theory of descent 

 and hitherto generally employed, must be abandoned. 



* Marsh represents the same view of the question on tlie basis of his 

 palceontological investigations; vide Marsh, '•American Jurassic Mam- 

 mals," Amer. Jouru. of (Science, vol. xxxiii., 1887. 



