34 EVOLUTION AND MAN S PLACE IN NATURE 



poles of the spindle and form the nuclei of two new cells. 

 This brief summary represents in outline the results of 

 the closest observation of procedure in Nature s labora 

 tory, where expansion of life occurs. Young cells 

 arise from a parent cell by division of the nucleus, fol 

 lowed by cleavage of the cell protoplasm, so that each 

 cell is directly descended from a pre-existing cell. 1 



Microscopic cells, such as those described, contain 

 the living principle in the tissues equally of vegetable 

 and animal forms. The two kingdoms have thus a 

 common basis in the protoplasm which is their essen 

 tial condition. In the fixed order of Nature, the 

 vegetable kingdom is that which is capable of pro 

 ducing protoplasm. Notwithstanding all the funda 

 mental resemblances which exist between the powers 

 of protoplasm in plants and in animals, they present 

 a striking difference in the fact that plants can manu 

 facture fresh protoplasm out of mineral compounds, 

 whereas animals are obliged to procure it ready made, 

 and hence in the long run depend upon plants. 2 



We follow Nature s line of progression in rising 

 from the simple cell to the germ cell or egg, which 

 constitutes the first stage of embryonic existence for 

 the animal. This introduces distinction of sex in the 

 work of reproduction. On this higher level, each type 

 of life springs from a fertilised egg. The ovum is ferti 

 lised by addition of the spermatozoon. In every such 

 egg there is nutritive material, and a nucleus which 

 is the centre of reproductive activity. This nucleus 

 carries within it the characteristics of the species to 

 which it belongs, illustrating heredity. Thus, when 

 differentiation of sex has appeared, each parent con- 



1 The. Cell Theory, p. 35. * Huxley s Lay Sermons, p. 138. 



