THE ANIMAL KINGDOM. 



All of the different forms already enumerated both 

 protozoan and metazoan are called animals,* in contrast 

 with another great group of living forms, the plants, which 

 form the Vegetable Kingdom. 



At first sight the animals and the plants seem entirely 

 distinct. "We say that animals move, have sensation, have 

 organs of feeding, of respiration, motion, etc., and that the 

 plants lack all these. When we contrast a cat and a cab- 

 bage these and many other points of difference are at once 

 forced upon us, while the features in which they resem- 

 ble one another seem to be extremely few. When, how- 

 ever, we carry our comparisons farther and take the lower 

 forms into account we soon find that these distinctions fail. 

 We find many animals which are as firmly fixed as any 

 tree, while we find many undoubted plants which move 

 through the water as freely as any fish. We find, again, 

 many plants which have undoubted powers of sensation. 

 House-plants in a window turn their leaves towards the 

 source of light; the leaves of the sensitive-plant droop if 

 they be touched; while the reproductive elements (zoo- 

 spores) of many low aquatic plants will recognize the pres- 

 ence of and swim towards a trace of malic acid. On the 

 other hand, sensory organs are as poorly developed in 

 sponges, and in many Protozoa, as in many plants. 



* Frequently the term animal is restricted to members of the group 

 of mammals. Thus we hear one say "animals and birds." This is 

 not correct. A bird, a fish, or a clam is as truly an animal as a cat. 



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