1 68 The Study of Animal Life PART in 



Diverse as are the styles of animal and vegetable archi- 

 tecture, the materials are virtually the same, and the 

 individuals 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 analogous manufac- 

 tories, 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 begins to divide after it has been penetrated, 

 and in some subtle way stimulated, by a male unit or sperm. 

 The great facts of individual history or development then 

 are, the apparent simplicity in the beginning, the pre- 

 liminary condition that the egg-cell be united with a male 



