MODERN BIOLOGY 513 



of inorganic nature is divided into mineralogy, hydrology, and meteorology; 

 and biology is divided into xpology, -protistology, and botany. Thus we have 

 here four threefold groups, all extremely ill-grounded. One is tempted to 

 assume that it is really Schelling's romantic ternary mysticism haunting 

 him here — though, of course, indirectly and unconsciously. The division 

 into plants, animals, and protista is, of course, entirely useless, nor did it 

 ever succeed; instead of one vague line of demarcation such as that between 

 plants and animals, we here get two. Then the aims and means of morphol- 

 ogy are described; the aim is a mechanically causal explanation of the forms 

 and phenomena of life, whereby a "monistic" explanation of the universe 

 will be made possible, which indeed, it is declared, is already so in the 

 other natural sciences, but in biology is for the time being replaced by a 

 "vitalistic" and "dualistic" view, the incorrigibility of which is depicted 

 in vivid colours. The means of attaining this monistic explanation of nature 

 is declared to be by "philosophical thinking," by the aid of which, facts 

 should be capable of interpretation, whereas the mere observation of nat- 

 ural phenomena is deeply despised. As a matter of fact, this philosophizing 

 constitutes Haeckel's great weakness, which gradually induces him to aban- 

 don exact research. The insistence upon interpreting the phenomena of life 

 according to purely mechanical laws is in itself fully justified; physiology 

 had already pursued that method before Haeckel's time, and his claim that 

 the other branches of biology should follow its example was quite reason- 

 able. But Haeckel's great mistake lay in his refusal to realize and acknowl- 

 edge the limited possibilities of the mechanical explanation of nature. He 

 certainly admits in one passage (p. 105) that the human capacity for knowl- 

 edge has its limits: that we cannot reach the ultimate grounds for a single 

 phenomenon, and that the origin of a crystal down to its ultimate causes is 

 just as inexplicable as the origin of an organism. But he does not stop for a 

 moment to think that in such circumstances natural philosophy should en- 

 deavour to determine these limits and see that they are not exceeded. Shortly 

 after the above admission he confidently asserts that no essential difference 

 between animate and inanimate exists; after making a close comparison he 

 comes to the conclusion that the crystal and the living cell are in all respects 

 comparable, as to their physical and chemical composition, their growth and 

 individuality. The restriction that should follow from the limitation of the 

 human capacity for knowledge is entirely forgotten. The memory of it cer- 

 tainly reawakens now and then, but, generally speaking, he entertains a 

 blind faith in the power of "mechanical causality" to explain anything 

 whatever. 



Mechanical interpretation of nature 

 What Haeckel chiefly bases his conviction upon as to the unlimited possi- 

 bilities of the mechanical explanation of nature is Darwin's theory. His 



