Development of the Mammalian Phylum. 379 



Indeed, in one direction they even talk of the " futility of the 

 tlieovy of descent " ! 



How could this view have arisen ? In the first place it is 

 to be remarked that the so-called " morphologico-historical " 

 method is an artificially constructed conception, which by no 

 means coincides with tlie " phyloo-enetic " method, which is 

 nevertheless said to be intended thereby. It is undoubtedly 

 true that morphology has stood for a time in the foreground 

 and has been almost exclusively employed in phylogenetic 

 investigations. Since in addition to this isolated branches 

 of morphology were applied more or less exclusively to the 

 solution of phylogenetic problems, our science threatened to 

 become shallow. I need but allude to the innumerable 

 papers in the domain of embryology whicli apply their one- 

 sided results to phylogenetic specuhations. A deepening of 

 our science can only set in when not only the three branches 

 of morphology, comparative anatomy, embrj^ology and 

 palaeontology, but also physiology, are simultaneously 

 employed as roads to knowledge. The goal which we thus 

 attain to is the comprehension of the position of each animal 

 in nature, the determination of its relations to the surrounding 

 organic and inorganic world, and the discovery of laws of 

 constantly more general application which have governed the 

 organic genesis. Now, as ever, the problem of life itself 

 remains untouched by this method of investigation; in our 

 studies we reckon with the living properties of an organic 

 body as with a fact which we indeed have not explained, but 

 which is none the less cstablislied. 



The adherents of the new school, however, believe that 

 they are able to conduct this latter problem to its final solu- 

 tion if they apply the method which they have chosen, of 

 referring everything that happens in the animal body to 

 piiysico-chemical laws. But every animal body is the result 

 of two groups of forces, which form ;ind transform it. The 

 one is still unexplained, and was formerly termed vital force, 

 the other is the totality of the piiysico-chemical forces of the 

 outer world. In order to reach the goal which they are 

 striving after, the representatives of the new school completely 

 ignore the fact that in each organism, in each of its cells, 

 processes take place which we term life and cannot explain. 



Herein, therefore, lies the great error of the mcchanico- 

 etiological school, in believing that it is able to explain life 

 itself, while, on the contrary, its final aim can only be to 

 show how organic formations which are already in existence 

 are subject to the physico-chemical ibrces just as much as the 

 inorganic bodies. The new element whicli the meclianico- 



26* 



