CHAPTER XVII. 

 REPRODUCTION AND DEVELOPMENT. 



199. THE simplest method of multiplication observed in any 

 set of living bodies is by splitting up into different parts, each 

 of which becomes a distinct individual. This is called multi- 

 plication by fissiparous division, and is principally found in 

 the very simplest forms, such as unicellular organisms. It 

 is precisely the same mode of multiplication, occurring in 

 distinct beings, as that by which cartilage-corpuscles and 

 others increase in number. 



When small portions, or buds, are separated from a parent, 

 the mode of reproduction is said to be of a gemmiparous 

 description; and if the bud should happen to be only a single 

 nucleated corpuscle devoted to reproduction, separated from 

 a large mass of such corpuscles, or from an organism how- 

 ever complex, yet it is plain that it may be none the less 

 fairly considered as a bud or germ from the whole organism. 

 Now, that is precisely what an ovum essentially is : but an 

 ovum, whether vegetable or animal, has the peculiarity that 

 it will not develop into a new individual unless there be 

 incorporated with it another germ of dissimilar kind, though 

 derived from the same species of organism; and herein con- 

 sists the essence of sexual reproduction. The germ which 

 appears to retain its individuality before and after fertilization 

 is the ovum, or female element ; while that which disappears 

 by being incorporated therewith is the male element. 



200. In the present state of science no explanation can be 

 given why such a thing as sex should exist. It is difficult 

 to say how far down in the organic world the distinction of 

 sex extends, but it exists in organisms of exceedingly simple 

 character; and in those of more complex descriptions, although 

 in certain instances a series of generations are produced 



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