DIVISION OF LABOUR. 401 



into galleries or tubes, along which the food is con- 

 veyed from one part of the body to another. These 

 tubes are filled with blood, pumped backwards and 

 forwards by the heart. The muscles which move the 

 outer limbs are equipped with nerves, the movements 

 of which are directed from centres in the spine and 

 brain. The functions of rife are thus divided, and 

 each department has an organ of its own. The repro- 

 ductive function is divided farther still. Two separate 

 elements are formed ; one prepares and ejects the 

 sperm-cell which the other receives, and unites to the 

 germ-cell. At a later period in the History .of Life 

 this arrangement is supplanted by another, more com- 

 plicated still. The two elements no longer co-exist in 

 the same form, and thus reproduction can only be 

 effected by means of co-operation between two distinct 

 and independent individuals. How important a fact 

 is this will presently appear. 



These various inventions of Nature, so far as we 

 have gone ; the limbs of locomotion and prehension ; 

 the heart with its vessels ; the brain with its nerves ; 

 and the separation of the sexes, all occurred in the 

 marine period of the earth's life : in the dark deep 

 sea womb. 



Similar changes, but inferior in degree, occurred in 

 the vegetable world. The shapeless specks became 

 one-celled : they were next strung together like a chain 

 of beads ; they then grew into sea-weed and aqueous 

 plants, which floated about, and finally obtained a 

 footing on the land. But they dwelt long ages on the 

 earth before their sex appeared. There were no 

 flowers in that primeval world, for the flower is a sign of 

 love. Gigantic mosses and tree ferns clothed the earth, 

 and reproduced themselves by scattering cells around. 

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