140 GENERAL PRINCIPLES OF ZOOLOGY. 



boiled more than ten minutes before they are destroyed. As the final 

 result of all the recent experiments and observations it can only be said 

 that t\\Q present existence of spontaneous generation is not proved. Now 

 the question is, With what right can one conclude that spontaneous gene- 

 ration neither occurs nor has ever occurred ? 



First Origin of Life. Whoever, in agreement with the teachings of 

 astronomy, adopts the view that our earth was at one time in a molten 

 condition and has gradually cooled, must assume that life on the earth 

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

 If he wish to base his explanation, not upon a supernatural act of crea- 

 tion, nor upon hypotheses, like that of the transference of living germs- 

 from other worlds through the agency of meteors, there is left only the 

 hypothesis that, according to the generally prevailing and still to be 

 observed laws of chemical affinity, compounds of carbon, oxygen, hydro- 

 gen, nitrogen, and sulphur have been brought together to produce living 

 substance. This process is called spontaneous generation. If the carbon, 

 oxygen, nitrogen, etc., which are now combined in a stable manner in 

 organisms were formerly unstable, the conditions for the origin of organic 

 compounds, through whose wider combination life would be possible, may 

 have been more favorable. Thus the hypothesis of the first origin of life 

 through spontaneous generation is carried to a logical postulate. 



But the postulate cannot be extended to affirm that spontaneous gen- 

 eration must even now exist. Since there are neither observations nor 

 convincing theoretical considerations for such a view, there is no necessity 

 to discuss the objections here. 



II. GENERATION BY PARENTS, OR TOCOGONY. 



As mentioned above, we shall deal here only with those methods 

 of reproduction which have actually been observed, i.e., generation 

 by parents. These methods fall mainly into two great groups, 

 asexual and sexual generation, monogony and amphigony, to which 

 may be added a third group, a combination of these two methods 

 of reproduction. 



a. Asexual Reproduction. Monogony. 



Monogony Defined. The chief characteristic of asexual repro- 

 duction is the fact that for it only a single organism is necessary. 

 But since, in certain modes of sexual reproduction (herma- 

 phroditism, parthenogenesis), this also holds true, further explana- 

 tion is necessary. Asexual reproduction must be a result of the 

 growth of the organism. This growth may be general and result 

 in an equal growth of all parts; or it may be local and consequently 

 lead to the formation of an outgrowth in the region of greatest 

 increase. In the first case division takes place, in the latter 

 budding. 



