30 CHANGE 



type, or species, of its day. The testimony of the 

 rocks informs us, beyond the shadow of a doubt, 

 that at different periods of geological history the 

 fauna and flora of the earth were entirely different ; 

 that very few of the species now existing were 

 to be found during periods which, geologically 

 speaking, are not very remote, and that with the 

 progress of cycles the forms of animal and veget- 

 able life have advanced from the very simplest 

 to the complex developments of the present day. 

 It is true that in only a few cases have fossils 

 yielded us the actual links of a chain of evolution- 

 ary changes, to show the steps by which a tribe of 

 organisms has altered its form. The fossils of an 

 epoch are a miserably incomplete record of its 

 fauna : what, for instance, could we learn of the 

 bird-life of present-day England by scouring the bed 

 of the Thames ? But, in respect to a few animals, 

 such links are forthcoming. One of the earliest 

 forms of the horse whose fossil bones have been dis- 

 covered (Orohippus), possessed four toes ; fossils 

 that have been disinterred from later deposits 

 show very completely the absorption of the first 

 toe, and the gradual shortening of the second and 

 fourth toes until they only remain as rudimentary 

 " splint bones " in the horse of our time. 



Moreover, there has been a gradual change of 

 habitat : Life, beginning in the sea, has passed on 

 to the land and thence to the air, and animals 

 which for the most part inhabit one of these ele- 

 ments have shown a tendency to trespass upon the 

 others. Thus amongst mammals which are 

 mainly terrestrial whales and seals have taken 

 to water, and bats to air ; amongst birds, ostriches 

 have become purely terrestrial, penguins and 

 divers almost aquatic ; whilst frogs, and other 

 batrachians, pass a portion of their life in water 

 and another portion on land. 



