CHAPTER XXII 



REPRODUCTION 



IT is a fundamental truth that every living organism 

 has had its origin in some preexisting organism. The 

 doctrine of " spontaneous generation," or the supposed 

 origination of organized structures out of inorganic par- 

 ticles, or out of dead organic matter, has not yet been 

 sustained 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 reproduction there are two kinds Self- 

 division (Fission} and Budding. 



Self -division, the simplest mode possible, is a natural 

 breaking-up of the body into distinct surviving parts. 

 This process is sometimes extraordinarily rapid, the 

 increase of one animalcule (Paramecium) being com- 

 puted at 268 millions in a month. It may be either 

 transverse or longitudinal. Of the first sort, Fig. 10 is 

 an example ; of the latter, Fig. 1 1 , a. This form of re- 

 production is, naturally, confined to animals whose tis- 

 sues and organs are simple, and so can easily bear 

 division, or whose parts are so arranged as to be easily 

 separable without serious injury. The process is most 

 common in Protozoa, worms, and polyps. 



Budding is separated by no sharp line from self- 

 division. While in the latter a part of the organs of 

 the parent go to the offspring, in the former one or 



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