i THE WEALTH OF LIFE 13 



structure, it might also express our notions of the blood- 

 relationships of animals and of the way in which the 

 different forms have arisen. 



But the wealth of form is less varied than at first sight 

 appears. There is great wealth, but the coinage is very 

 uniform. Our first impression is one of manifold variety ; 

 but that gives place to one of marvellous plasticity when 

 we see how structures apparently quite different are re- 

 ducible to the same general plan. Thus, as the poet 

 Goethe first clearly showed, the seed-leaves, root-leaves, 

 stem-leaves, and even the parts of the flower sepals, 

 petals, stamens, and carpels, are in reality all leaves or 

 appendages more or less modified for diverse work. The 

 mouth-parts of a lobster are masticating legs, and a 

 bird's wing is a modified arm. The old naturalists were 



O 



so far right in insisting on the fact of a few great types. 

 4. Wealth of Numbers. Large numbers are so un- 

 thinkable, and accuracy in census-taking is so difficult, 

 that we need say little as to the number of different 

 animals. The census includes far over a million living 

 species a total so vast that, so far as our power of 

 realising it is concerned, it is hardly affected when we 

 admit that more than half are insects. To these recorded 

 myriads, moreover, many newly-discovered forms are 

 added every year now by the individual workers who 

 with fresh eye or improved microscope find in wayside 

 pond or shore pool some new thing, or again by great 

 enterprises like the Challenger expedition. Exploring 

 naturalists return from tropical countries enriched with 

 new animals from the dense forests or warm seas. Zoo- 

 logical Stations, notably that of Naples, are " register- 

 houses ' for the fauna of the neighbouring sea, not 

 merely as to number and form, but in many cases taking 

 account of life and history as well. Nor can we forget 

 the stupendous roll of the extinct, to which the zoological 

 historians continue to add as they disentomb primitive 

 mammals, toothed birds, giant reptiles, huge amphibians, 

 armoured fishes, gigantic cuttles, and a vast multitude 

 of strange forms, the like of which no longer live. The 

 length of the Zoological Record, in which the literature 



