16 



EVOLUTION AND ANIMAL LIFE 



trees, the hair of mammals, the feathers of birds, the body 

 tissues of mosquitoes, all places where animal life is found, are 

 being examined with an eagerness not less than that of the early 

 explorers, while the investigators of to-day are armed with 

 every appliance that science can devise. Yet now, as in Lin- 

 nseus's time, it is certain that not half of the number of species 

 of animal organisms is yet known. The 600,000, more or less, 



-SSS 



FIG. 5. Diamond rattlesnake, Croialus adamanteus. (Photograph by W. K. Fisher.) 



on our registers to-day are certainly far less than half of the 



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millions which actually exist. 



In botany we find the same conditions. There are fewer 

 known species of plants than animals by half, and they are more 

 easily preserved and handled, while the work of collection and 

 investigation proceeds on a scale even more extensive, yet it 

 would be a bold statement to say that we know to-day half the 

 species of plants that exist. 



All this refers to the forms now living, without reference to 

 the host which composes their long ancestry, extending back- 

 ward toward the dawn of creation. The species have come 

 down through the geological ages, changing in form and func- 

 tion to meet the varying needs of changing environment. This 



