THE SORTING OF PLANTS AND ANIMALS 73 



pearance of certain caterpillars is much like that of certain 

 worms ; indeed, many people call caterpillars worms ; but a 

 study of the structure at various stages in the course of the 

 organism's life — that is, its development— at once separates 

 the two groups. We find that the caterpillar is the young stage 

 of some insect (see page 30), whereas the worm never gets to 

 be anything but an older worm. iModern classification of organ- 

 isms accordingly considers all that can be known about living 

 things, and not merely their appearance or their uses. 



In recent times the study of classification has acquired new value be- 

 cause of the light it throws on problems of new species, and because of 

 its aid in the study of heredity and plant and animal breeding (see Chap- 

 ters XLV, XLVI). 



63. The basis of classification. We have divided all organisms 

 roughly into plants and animals, without trying to define either 

 of these terms. We really ought to know more about them 

 before we attempt any definition. Within each of these two 

 principal divisions it is possible to say in a general way that 

 a given species is "higher" or "lower" than another. Yet it is 

 impossible to place all the known plants (or all the known 

 animals) in a series from the'lowest to the highest. This would 

 be about as sensible, or as absurd, as trying to arrange all the 

 people in a series from the worst to the best. We find that 

 there are several main branches (among plants as well as 

 among animals), some of which v^^e should place higher and 

 some lower. But we find in each branch so many degrees of 

 complexity that there is considerable overlapping when it 

 comes to arranging all the organisms. The diagram on page 74 

 (Fig. 36) will give a general idea of the relationships of the 

 main branches of plants, and the one on page 75 (Fig. 37) will 

 suggest the same for the animals. 



"ftto" 



In placing here the general scheme of plant classification and that of 

 animal classification it is not intended that you should learn or memo- 

 rize them by study. There are many terms in the descriptions of the 

 various divisions and subdivisions which can have no meaning for the 



