THE GASTRAEA-THEORY, ETC. 149 



2. The Causal Significance of the Gastraea-theouy. 



The application of the general biogenetic principles to the 

 different departments of special biology, and especially to the 

 natural systems of organisms, is a scientific problem which, 

 it is true, must be claimed, as a matter of course, by all 

 thinking biologists, but wliich encounters the greatest diffi- 

 culties at every attempt to carry it thoroughly into execution. 

 These difficulties in general chiefly depend on the low condi- 

 tion of development of our biological knowledge, on the little 

 participation which biology has hitherto had in the funda- 

 mental formative developmental functions of inheritance and 

 adaptability, but more especially on the great deficiencies 

 and incompleteness of the empirical so-called " records of 

 creation" which the three schools of ontogenesis, palgeon- 

 tology, and comparative anatomy ofier us. 



In spite of these great obstacles and difficulties, the import- 

 ance of which I do not lose sight of, I have ventured, in 

 1866, in my ' General Morphology,' to make a first attempt to 

 arrive at the natural system of organisms with the help of 

 the biogenetic principles of the theory of descent, and in the 

 " Systematic introduction to the general history of develop- 

 ment" (vol. 2, pp. xvii — clx) to establish phylogenesis as the 

 basis of the natural system. I have renewed and improved 

 this attempt in a more popular form in my ' Naturlichen 

 Schopfiingsgeschichte ' (1868; 4th ed., 1873). But, never- 

 theless, these first attempts (as I expressly designated 

 them from the beginning) have, with few exceptions, 

 encountered only lively disapproval and decided disap- 

 probation among my immediate colleagues; but no one 

 has troubled himself to supersede my phylogenetic system by 

 a better one. This problem lies before any one who admits 

 the theory of descent, and aims at a causal comprehension of 

 organic forms. ^ 



' The best defence against the numerous attacks which my phylogenetic 

 system of organisms has endured seems to me to be that I am always trying 

 to improve it, and thus to arrive at an understanding of the causal connection 

 of the organic form, which cannot be arrived at in any other way. The 

 altaclis of Riitimeyer, one of the most energetic of my opponents, in whose 

 opinion my genealoj<ical tree does not agree with Darwinism and the theory 

 of descent, ha've been already disposed of in the preface to the third edition of 

 the ' Naturlichen Scboijfiingsgeschichte.' It is enough at present to quote 

 the naive sentence in which Riirimeyer himself a|)tly characterises his com- 

 prehension of the theory of descent : — "Darwin's views appear to me to be 

 a species of naturalist's religion, which we can only be for or against, but 

 the odium theologicum is admitted as a proverb, and I do not, therefore, 

 imagine that much can come of it." 



