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CHAPTER IX. 

 KEPEODUCTION AND HEREDITY. 



THE last chapter gave us an insight into the marvels of 

 reproduction of the lowest forms of animal life. Though the 

 conditions were simpler the questions were essentially the same 

 that confronted us in the reproduction of the higher and highest 

 animals. Death, which only makes a shy attempt to establish 

 its dominion over the lowest forms, now never ceases to hold 

 its victim in a firm grasp. Individuals come and go; only the 

 germ-cells guarantee the continuity of life and make the charac- 

 ters of the parents reappear in their descendants. If sexual 

 union played a comparatively inferior role in the unicellular 

 organisms it now rules the entire life. Love now becomes 

 an omnipotent factor which brings together the two sexes 

 with elemental force. In addition we observe a new factor : 

 the care of the parent for the offspring. There are, of 

 course, many multicellular animals which, having deposited 

 the ova, do not take any further interest in them, but the 

 higher we ascend in the animal world, the greater the solicitude 

 demanded by the young brood, the longer are the parents 

 compelled to look after the young, jointly or separately, until 

 they have at last acquired the necessary strength and skill to 

 join in the struggle for existence. In many of the higher 

 animals and man, this union of parent and offspring may even 

 become so complete that it will end only with the death of 

 the progenitor. 



The jump from the protozoa to the higher animals is not so 

 great as would at a first glance appear, for the two great kingdoms 

 are connected by gradual transitions : organisms of more than 

 one cell. Farther, the lowest multicellular animals as yet 

 occupy in their whole organization a very low stage, enormous 

 though the progress they represent, compared with the organisms 



