344 THE WORLD OF LIFE CHAP 



may be called the mechanical explanation of heredity by 

 means of the successive changes observed in the growing 

 and dividing germ -cells. But, as he himself admits, it 

 explains nothing without taking for granted the essential 

 phenomena of life nutrition, assimilation, and growth ; and 

 these are admitted to be to this day quite unexplainable. 



But the very first step of this process of growth the 

 division of the germ-cells, as described by Weismann himself 

 and illustrated by his diagrams is, as he himself almost 

 admits, equally inexplicable. He speaks of a " complex, but 

 wonderfully exact, apparatus for the division of the nucleus," 

 of the purpose of that division being qualitative as well as 

 quantitative, and of its evident adaptation to the building 

 up of the future body, with all its marvellous complexities, 

 co-ordinations, and powers. So that the farther we go 

 in this bewildering labyrinth, as expounded in his works, in 

 those of Professor Thomson, of Max Verworn, or in such 

 general works as Parker and Haswell's Text-Book of Zoology, 

 the more hopelessly inadequate do we find the claims of 

 Haeckel, Verworn, and their school to having made any 

 approach whatever to a solution of "the riddle of the uni- 

 verse," so far as regards its crowning problem, the origin and 

 development of life. 



The Plant Cell 



So far I have taken the facts as to cell-division from the 

 works of zoologists only ; but almost exactly the same 

 phenomena have been found to occur in plants, though they 

 seem to have been rather more difficult to detect and unravel. 

 In Professor A. Kerner's Natural History of Plants, already 

 quoted, he gives the following short description of cell- 

 division : 



" When a protoplast living in a cell-cavity is about to divide into 

 two, the process resulting in division is as follows : The nucleus 

 places itself in the middle of its cell, and at first characteristic lines 

 and streaks appear in its substance, making it look like a ball made 

 up of little threads and rods pressed together. These threads 

 gradually arrange themselves in positions corresponding to the 

 meridian lines upon a globe ; but at the place where on a globe 

 the equator would lie, there then occurs suddenly a cleavage of the 



