CHAPTER XXXIX. 

 REPRODUCTION. 



Reproduction in General. In all cases reproduction 

 consists, essentially, in the separation of a portion of living 

 matter from a parent; the separated part bearing with it, or 

 inheriting, certain tendencies to repeat, with more or less 

 variation, the life history of its progenitor. In the more 

 simple cases a parent merely divides into two or more pieces, 

 each resembling itself except in size; these then grow and 

 repeat the process; as, for instance, in the case of Amoeba and 

 our own white blood corpuscles (pp. 23, 44). Such a process 

 may be summed up in two words as discontinuous growth; 

 the mass, instead of increasing in size without segmentation, 

 divides as it grows, and so forms independent living beings. 

 In some tolerably complex multicellular animals we find 

 essentially the same thing; at times certain cells of the fresh- 

 water Polype multiply by simple division in the manner 

 above described, but there is a certain concert between them: 

 they build up a tube projecting from the side of the parent,. a 

 mouth-opening forms at the distal end of this, tentacles 

 sprout out around it, and only when thus completely built up 

 and equipped is the young Hydra set loose on its own career. 

 How closely such a mode of multiplication is allied to mere 

 growth is shown by other polypes in which the young, thus 

 formed, remain permanently attached to the parent stem, so 

 that a compound animal results. This mode of reproduction 

 (known as gemmation or budding) may be compared to the 

 method in which many of the ancient Greek colonies were 

 founded; carefully organized and prepared at home, they 

 were sent out with a due proportion of artificers of various 

 kinds; so that the new commonwealth had from its first sep- 

 aration a considerable division of employments in it, and was, 

 on a small scale, a repetition of the parent community. In 

 the great majority of animals, however (even those which at 

 times multiply by budding),'a different mode of reproduction 



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