84 The Insides and the Workjngs of Living Things 



as are the highest. The ameba, for example, although it has 

 no mouth, is able to take into itself what it needs in the way 

 of food. Although it has no stomach, it is able to digest 

 what it takes in as effectively for its needs as does a fish or 

 a pig. Although it has neither lungs nor gills, it manages 

 to get from its surroundings the oxygen it needs and to dis- 

 charge, without any special breathing organs, the waste 

 products of combustion. Although it has no muscles or 

 limbs, no tail or fins, it can both swim and crawl. Without 

 sense organs or nerves or brain it manages somehow to find 

 what it needs and to escape injury — at least sufficiently to 

 preserve the species from extermination. Although it has 

 no special organs of reproduction it manages to leave off- 

 spring, notwithstanding that the individual, in reproducing, 

 destroys his own identity. 



The simplest plants likewise show adequate adaptation 

 to the conditions under which they live, without any of the 

 special organs that characterize higher forms. Some plants 

 apparently can live without roots, stems or leaves, just as 

 some animals can live without stomachs and livers and lungs. 



Function 'Precedes Structure 



From a study of the simplest plants and animals now 

 living we come to realize that the essential functions of liv- 

 ing things can be carried on in the absence of the special 

 structures or organs which we have come to associate with 

 those functions. To say that " function precedes structure " 

 is merely to describe the facts, so far as they can be observed 

 in any of the higher individuals that have special organs. 

 The developing embryo digests food long before it has a 

 stomach. It absorbs oxygen, utilizes it, and discharges car- 

 bon dioxid and other oxids, long before it has anything cor- 

 responding to a lung or a gill. It contracts in one part or 

 another before there are any " muscles." It is sensitive to 

 changes in external conditions before it elaborates nerves 

 or sensory organs. Similarly we find that the " lowest " or 



