MODERN BIOLOGY 519 



far-fetched homologization of the germinal layers has been considerably re- 

 stricted, the same organs in a number of different animal forms having been 

 found to possess an entirely different origin. In particular, the mesodermal 

 formation has now been resolved into a number of different processes. In 

 fact, the entire " biogenetical principle" is nowadays severely challenged, 

 even as a hypothesis; in the vegetable kingdom it has received no confirma- 

 tion, which is indeed strange for a theory proposed to hold good as a gen- 

 eral explanation of life, but even those zoologists who in general give any 

 support at all to the recapitulation theory do so with considerable reserva- 

 tions, called for by the results of modern hereditary research and experi- 

 mental biology. Nowadays one does not compare without question, as they 

 did in Haeckel's time, the ideas of similarity and affinity ; similarity can 

 demonstrably arise through the influence of very different factors, and it is 

 preferred to follow His in seeking for the mechanical conditions governing 

 the development of form instead of seeing therein resemblances to the ani- 

 mal life of past ages. But this should not involve our depreciating Haeckel's 

 influence on the development of embryology; it was his theory which evoked 

 that interest in those phenomena that brought about the immense revival 

 of this form of research, lasting up to the present day. In this connexion we 

 may remember von Baer's words that "inaccurate but definitely pronounced 

 general results have, through the corrections which they call for and the 

 keener observation of all the circumstances which they induce, almost in- 

 variably proved more profitable than cautious reserve." It is just herein that 

 Haeckel has benefited his science most; here he has made his most important 

 and historically most yaluable contribution. But with it he gave all that 

 he had to give; the years that he lived afterwards produced nothing to in- 

 crease his reputation, but detracted much from it. 



His ivork on ' ' peri genes is 

 For as early as in his Antbropogeny Haeckel displays his increasing weakness 

 for vague and profitless speculations. Talk of a mechanical explanation of 

 nature is certainly kept up, but it becomes more and more empty w^ords, 

 while the spiritual qualities of matter appear increasingly in the foreground; 

 energy and soul are now consistently identified, and are generally denoted 

 by the term "energy," in a manner which testifies to his absolute contempt 

 for the simplest grounds of physics. And this fault is still more intensified 

 in a treatise published in 1875 entitled Die Ferigenesis der Plastidule, the nat- 

 ural-philosophical confusion pervading which it is truly difficult to repro- 

 duce in a summary. The title itself is supposed to mean " the wave-production 

 of life-particles" and this is intended to explain the same phenomena as 

 those upon which Darwin tries to throw light by means of his pangenesis 

 theory — that is, heredity and adaptation. The pangenesis theory fails to 

 satisfy Haeckel, who instead endeavours to explain heredity by an analysis 



