THE WONDERS OP LIFE 



view of the functions they have to discharge, and the 

 regularity of their construction in the unity of the his- 

 ton — in other words, their adaptive organization — ^is 

 explained mechanically by the theory of selection, while 

 the teleological hypotheses of dualistic biology (for in- 

 stance, the "intelligent dominants" of Reinke) com- 

 pletely fail to account for their origin. The gradual 

 advance of the organs and their physiological division 

 of labor have many analogies in the two kingdoms of 

 the histona. While at the lowest stages the simple 

 organ represents only a separate individual piece of 

 primitive tissue, we find special systems of organs and 

 organic apparatus in the higher stages. 



The idea of a particular system of organs is deter- 

 mined by the unity of one tissue which forms the char- 

 acteristic element in the totality of the organs that be- 

 long to it. Of such systems in the kingdom of the 

 metaphyta we have: the skin-system (with the tissue 

 of the epidermis), the vascular system (with its con- 

 ducting and vascular fibres), and the complementary 

 tissue system (with the basic tissue). In the kingdom 

 of the metazoa we may similarly distinguish: the skin- 

 system (integument of the epidermis), the vascular sys- 

 tem (with the mesenchyma-tissue of the blood and 

 blood-vessels), the muscular system (with the muscle- 

 tissue), and the nervous system (with the neurona of 

 the nerve-tissue). 



In contrast with the histological idea of a system of 

 organs, we have the physiological conception of an ap- 

 paratus of organs. This is not determined by the unity 

 of the constituent tissue, but by the unity of the life- 

 work that is accomplished by the particular group of 

 organs in the histona. Such an apparatus of organs is, 

 for instance, the flowers and the fruit developing there- 

 from in the phanerogams, or the eye or the gut of an 

 animal. In these apparatus the most diverse organs 



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