REPRODUCTION. 



191 



CHAPTER XIX. 



REPRODUCTION. 



It is a fundamental truth that every living organism 

 has had its origin in some pre-existing organism. The 

 doctrine of " spontaneous generation," or the supposed 

 origination of organized structures out of inorganic parti- 

 cles, or out of dead organic matter, has not yet been sus- 

 tained by facts. 



Reproduction is of two kinds — sexual and asexual. 

 All animals, probably, have the first method, while a very 

 great number of the 

 lower forms of life have 

 the latter also. 



Of asexual reproduc- 

 tion there are two kinds 

 — Self - division and 

 Budding. 



Self-division, the 

 simplest mode possible, 

 is a natural breaking-up 

 of the body into distinct 

 surviving parts. This 

 process is sometimes ex- 

 traordinarily rapid, the 

 increase of one animal- 

 cule (Paramoecium) be- 

 ing computed at 

 millions in a month. It 

 may be either transverse or longitudinal. Of the first 

 sort, Figs. 1,2, and 3 (Fig. 160) are examples; of the latter, 



268 Pig- 160.— Reproduction of Infusoria (Vorticel- 

 Ice and others) by fission or self-division. 



