GENERAL EMBRYOLOGY 127 



can, for instance, regenerate lost appendages, the mammals have the regenera- 

 tive powers reduced to the healing of wounds. In metamerism a phenomenon 

 is repeated which obtains widely in the animal kingdom, and contributes 

 towards its higher development; first there is a reduplication of part (here the 

 segments), then a division of labor, so that the final result is a whole comj>osed 

 of many parts, but a singly organized whole. 



II. GENERAL EMBRYOLOGY. 



Origin of Organisms. Since the development of every individual 

 begins with an act of generation, the ways by which new organisms may 

 arise comes first. Admitting only that which has been actually observed, 

 we must cling to the aphorism of Harvey, "Omne vivum ex ovo," 

 altering it to Omne vivum e vivo: every living organism is derived from 

 another living organism. We must limit ourselves to the mode of origin 

 which has been termed tocogony, or generation by parents. The great 

 importance which the question of generation without parents, or spon- 

 taneous generation, has obtained through the evolution theory renders a 

 consideration of this question necessary at this point. 



I. GENERATIO SPONTANEA (ARCHEGONY, ABIOGENESIS). 



The old zoologists, including Aristotle, believed that many animals, 

 even frogs and insects arose spontaneously from the mud. This was not 

 disproved until the seventeenth and eighteenth centuries, and even then 

 the idea of spontaneous generation still held, especially for parasites, for 

 in the history of each animal there was a time when it contained none of 

 these, and they were supposed to arise from the superfluous plastic mate- 

 rial of the host. Later it was found how the eggs obtained entrance, 

 and then the idea of abiogenesis persisted only for microscopic organisms. 

 Water, which contained no living thing, after standing a while, was found 

 to contain organisms. Lastly it was discovered that these 'do not arise 

 dc noi'o, but come from minute germs, carried by the winds, or distributed 

 in other ways. If the fluids and the utensils are heated, and germs are 

 prevented from entrance by proper means, no life will appear, even if the 

 medium be kept for years. So it may be said, as the result of all recent 

 experiment, that the present occurrence of spontaneous generation is not 

 proved. 



First Origin of Life. If we adopt the view that our earth was at one time 

 in a molten condition and has gradually cooled, we must assume that life has 

 not existed on the earth from eternity, but at some time has had its beginning. 

 If we wish to base our explanation, not upon a supernatural act of creation, 

 nor upon hypotheses like that of the transference of living germs from other 

 worlds by meteors, there is left only the hypothesis that compounds of carbon, 



