1-22 



THE AMERICAN NATURALIST 



[Vol. XLVI 



proved indurable, whereas Loeb 6 lias pointed out that 

 faulty organisms must frequently arise, although we only 

 become aware of them under exceptional conditions. 



Moenkhaus found ten years ago that it is possible to fertilize the 

 egg of each marine bony fish with sperm of practically any other marine 

 bony fish. His embryos apparently lived only a very short time. This 

 year I succeeded in keeping such hybrid embryos between distantly 

 related bony fish alive for over a month. It is therefore clear that it 

 is possible to cross practically any marine teleost with any other. 



The number of teleosts at present in existence is about 10,000. If 

 we accomplish all possible hybridization 100,000,000 different crosses 

 will result. Of these teleosts only a very small proportion, namely, 

 about one one-hundredth of one per cent., can live. It turned out in 

 my experiments that the heterogeneous hybrids between bony fishes 

 formed eyes, brains, ears, fins and pulsating hearts, blood and blood 

 vessels, but could live only a limited time because no blood circulation 

 was established at all— in spite of the fact that the heart beat for 

 weeks— or that the circulation, if it was established at all, did not last 

 long. 



The possibility of hybridization goes much further than we have 

 thus far assumed. We can cause the eggs of echinoderms to develop 

 with the sperm of very distant forms, even mollusks and worms 

 (Kupelwieser) : but such hybridizations never lead to the formation of 

 •lur.-iMt* nro-anisms. 



It is therefore no exaggeration to state that the number of species 

 existing to-day is only an infinitely small fraction of those which can 

 and possibly occasionally do originate, but which escape our notice 

 because they can not live and reproduce. Only that limited fraction 

 of species can exist which possesses no coarse disharmonies in its auto- 

 matic mechanism of preservation and reproduction. Disharmonies and 



systems the rare exception. But since we only perceive the latter we 

 gain the erroneous impression that the " adaptation of the parts to the 

 plan of the whole " is a general and specific characteristic of animate 

 nature, whereby the latter differs from inanimate nature. 



If the structure and the mechanism of the atoms were known to us 

 we should probably also get an insight into a world of wonderful 

 harmonies and apparent adaptations of the parts to the whole. But in 

 this case we should quickly understand that the chemical elements are 

 d"^ bl^ feW b durable s >' stems among a large number of possible but not 



(c) Overlooking for the moment the obvious difficul- 

 ties of the assumption, we can be certain that the idea of 



