CHAP, xi THE ELEMENTS OF STRUCTURE 189 



simplest animals. For the tree of life is double like the 

 letter V, with divergent branches, the ends of which, 

 represented, let us say, by a daisy and a bird, are far 

 apart, while the bases gradually approach and unite in 

 a common root. 



Plants and animals are alike, though not equally, alive. 

 Diverse as are the styles of animal and vegetable architec- 

 ture, the materials are virtually the same, and the indi- 

 viduals in both cases grow from equally simple beginnings. 



Even movement, the chief characteristic of animals, 

 occurs commonly, though in a less degree, among plants. 

 Young shoots move round in leisurely circles, twining 

 stems and tendrils bend and bow as they climb, leaves 

 rise and sink, flowers open and close with the growing 

 and waning light of day. Tendrils twine round the 

 lightest threads, the leaves of the sensitive plant respond 

 to a gentle touch, the tentacles of the sundew and the 

 hairs of the fly-trap compare well with the sensitive 

 structures of many animals. The stamens of not a few 

 flowers move when jostled by the legs of insects, and the 

 stigma of the musk closes on the pollen. 



Plants and animals alike consist of cells or unit masses 

 of living matter. The structure of the cell and the 

 apparent structure of the living stuff is much the same in 

 both. We may liken plants and animals to two analo- 

 gous manufactories, both very complex ; we study the 

 raw materials which pass in, many of the stages and 

 by-products of manufacture, and the waste which is laid 

 aside or thrown out, but in neither case can we enter the 

 secret room where the mystery of the process is hidden. 



In the pond we find the eggs of water-snails and water- 

 insects attached to the floating leaves of plants ; in the 

 ditches in spring we see in many places the abundant 

 spawn of frogs and toads ; we are familiar with the 

 heavily yolk-laden eggs of birds. Now, with a little 

 care it is quite easy to convince ourselves that an egg 

 or ovum is to begin with a simple mass of matter, in 

 part, at least, alive, and that by division after division 

 the egg gives rise to a young animal. We are also well 

 aware that in most cases the egg-cell, for cell it is, only 



