CHAPTER XXXVII. 

 REPRODUCTION. 



ORIGIN OF MALE AND FEMALE GENERATIVE ELEMENTS. 



One of the chief characteristics of a living being is the power 

 it possesses of reproducing itself; that is to say, organisms can, 

 under favorable conditions, form out of themselves other living 

 bodies with similar lives and habits. 



In the lowest form of animal life this propagation of species 

 may take place by the division of a single cell ; thus, an amoeba 

 reproduces its like by the cleavage of its mass of protoplasm, 

 which separates the main body into two amoebae. In such a case 

 the method of reproduction is purely asexual, the amoeba con- 

 taining within itself the power of forming other amoebae without 

 help from other individuals. 



As we ascend the animal scale, we find that just as other func- 

 tions are allotted to certain groups of cells, specially differentiated 

 for the purpose, so the function of reproduction is performed by 

 certain specially modified collections of cells. Further, we find 

 the fact that the production of a new being requires the coopera- 

 tion of two kinds of generative elements, each of which is com- 

 monly produced by a different reproductive organ. These repro- 

 ductive organs in the higher animals are placed in different indi- 

 viduals of the same species. This divides most organisms into 

 male and female sexes, and is hence termed the sexual method of 

 reproduction. 



The sexual method of reproduction is met with in all the more 

 highly-developed forms of animal and vegetable life. The male 

 organ produces active elements the spermatozoa; the female 

 organ produces the ovum, which, when fertilized by the sperma- 

 tozoa, develops into the embryo. 



In mammalia the uterus is the most important of the subsidiary 

 organs, as it is modified for the development and growth of the 

 embryo ; its function, however, can be performed by other organs, 



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