The Mechanistic Conception of Life 25 



can live. It turned out in my experiments that the heterogene- 

 ous 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 

 — 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. 



What prevented these heterogeneous fish embryos from 

 reaching the adult stage? The lack of the proper "domi- 

 nants"? Scarcely. I succeeded in producing the same type 

 of faulty embryos in the pure breeds of a bony fish (Fundulus 

 heterocUtus) by raising the eggs in 50 c.c. of sea-water to which 

 was added 2 c.c. 1/100 per cent NaCN. The latter substance 

 retards the velocity of oxidations and I obtained embryos 

 which were in all details identical with the embryos produced 

 by crossing the eggs of the same fish with the sperm of remote 

 teleosts, e.g., Ctenolabrus or Menidia. These embryos, which 

 lived about a month, showed the peculiarity of possessing a 

 beating heart and blood, but no circulation. This suggests 

 the idea that heterogeneous embryos show a lack of '^ adapta- 

 tion" and durability for the reason that in consequence of the 

 chemical difference between heterogeneous sperm and egg the 

 chemical processes in the fertilized egg are abnormal. 



The possibility of hybridization goes much farther 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 durable organisms. 



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

 species existing today is only an infinitely small fraction of 

 those which can and possibly occasionally do originnte, but 

 which escape our notice because they cannot live and reproduce. 

 Only that limited fraction of species can exist which possesses 

 no coarse disharmonies in its automatic mechanism of preserva- 

 tion and reproduction. Disharmonies and faulty attempts in 



