PLANT AND ANIMAL COMPARED. 153 



function of the plant. If we may paraphrase the words of 

 Michael Foster, the oosphere is the goal of individual existence, 

 and life is a cycle, beginning with the oosphere and continually 

 coming round to it again. 



Comparison of the Fern and the Earthworm. To the super- 

 ficial observer the fern and earthworm seem to have little or 

 nothing in common, except that both are what we call alive. But 

 whoever has studied the preceding pages must have perceived 

 beneath manifold differences of detail a fundamental likeness 

 between the plant and animal, not only in the substantial iden- 

 tity of the living matter in the two but also in the construction 

 of their bodies and in the processes by which they come into 

 existence. Each arises from a single cell which is the result of 

 the union of two differently-constituted cells, male and female. 

 In both the primary cell multiplies and forms a mass of cells, at 

 iirst nearly similar but afterwards differentiated in various di- 

 rections to enable them to perform different functions, i.e., to 

 effect a physiological division of labor. In both, the tissues thus 

 provided are associated more or less closely into distinct organs 

 and systems, among which the various operations of the body 

 are distributed. And in botli the ultimate goal of individual 

 existence is the production of germ-cells which form the start- 

 ing-point of new and similar cycles. 



This fundamental likeness extends also to most of the actions 

 (physiology) of the two organisms. Both possess the power of 

 adapting themselves to the environments in which they live. 

 Both take in various forms of matter and energy from the en- 

 vironment, build them up into their own living substance, and 

 finally break down this substance more or less completely into 

 isimpler compounds by processes of internal combustion, setting 

 free by this action the energy which maintains their vital ac- 

 tivity. And, sooner or later, both give back to the environment 

 the matter and energy which they have taken from it. In other 

 words, both effect an exchange of matter and of energy with 

 the environment. 



Nevertheless the plant and the animal differ. They differ 

 widely in form, and the plant is fixed and relatively rigid, while 

 the animal is flexible and mobile. The body of the plant is 

 relatively solid ; that of the animal contains numerous cavities. 



