340 GENERAL PBINCIPLES 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 

 tliat the present existence of spontaneous generation is not proved. Now 

 the question is, With what right can one conclude tliat 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 tliat life on the earth 

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

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

 tion, nor upon hypotheses, like that of tlie 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, Tiitrogen, 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 unstaljle, tlie 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 postidate. 



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 liere. 



II. Generation" :!Y Pakekts, or Tocogoxy. 



As me7itioned above, we shall deal here only with those methods 

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

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

 asexual and sexual generation, monor/oiuf and ampJiic/oni/. to wliich 

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

 of reproduction. 



a. Asexual Eeproducfion. Jfonogoii//. 



Monogony Defined. — The chief characteristic of asexnal 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 liolds true, further explana- 

 tion is necesisary. Asexual reproduction must l)c a result of the 

 growth of the organism. This growth may l)e general and result 

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

 lead to the fornn^tion of an outgrowth in the region of n'reatest 

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

 bnddinff. 



