HIGHER ANIMALS AND PLANTS CONTRASTED 107 



extent, but worms and insects feed upon leaves and other 

 vegetable matter, so this food is only one step removed from 

 green matter. Man eats fish, oysters and other marine food ; 

 the larger fish eat smaller ones, these still smaller and so on until 

 the smallest eat Crustacea, larvae, and other micro-organisms 

 which as with rotifers, subsist finally on microscopic algae and 

 bacteria. Carnivorous animals live almost entirely without 

 green plants or their products and with them the ultimate 

 plant-eating forms serving as food are still more remote but in 

 the end we find the same dependence upon the vegetable world 

 for proteids and potential energy. 



The plant forms serving as food for the higher animals are far 

 more complicated than Pleurococcus and Sphaerella and just 

 as the higher animals become progressively differentiated with 

 complicated organs for the performance of the functions of food 

 getting, digestion, assimilation, excretion, nervous response 

 and reproduction so do the higher plants become progressively 

 differentiated with complicated organs for the performance 

 of their metabolic and reproductive functions. 



The lines of development of the two great kingdoms are 

 widely different. While at bottom the vital activities of plants 

 and animals are the same, the structural differentiations have 

 followed lines of entirely different requirements. Those of 

 animals have been directed toward food getting and food 

 digestion and protection against enemies who would make food 

 of them, functions involving highly developed muscular sys- 

 tems, closely correlated nervous responses, and centralized 

 nervous systems, and complicated organs for the digestion of 

 many different kinds of food. Their metabolism, therefore, 

 involves active destructive processes and the formation of 

 excessive waste matters for the disposal of which complicated 

 excretory organs have been evolved. Higher plants on the 

 other hand are stationary; their food material being everywhere 

 about them locomotor organs are not developed, their nervous 

 response is limited to protoplasmic irritability; waste matters 

 are relatively unimportant and easily disposed of requiring no 

 complicated excretory organs. Their plan of development, 



