A VIEW IN PERSPECTIVE. IIQ 



animals with simple structure are not so delicately 

 adapted to their environment as to require a change 

 for every little change in their surroundings. The 

 higher animals, however, are so complex and withal 

 so delicately adjusted to their environment that any 

 little change of conditions throws them out of har- 

 mony, and requires change in structure to meet the 

 new conditions. A steam engine requires much 

 more care and gets out of order more readily 

 than a water-wheel. So the types of low animals 

 have continued to exist, while the higher ones have 

 been rapidly modified. 



(7 It is to be noticed further that not only has this 

 Change of species been a constant change, but that 

 itrias also been a gradual one. There have proba- 

 bly been no abrupt breaks in the history. We find 

 that when one species disappears, it is either re- 

 placed by another^closely related form, or the whole 

 line becomes extinct. In all cases where the rocks 

 have preserveo! for us anything like a continuous 

 history, it is seen that there are no abrupt transi- 

 tions from one type to a radically different one. In 

 the few cases where the record is exceptionally com- 

 plete, it is possible to trace one species into another 

 by innumerable connecting links. Such evidence 

 is, however, rarely forthcoming, and new species 

 commonly seem to appear abruptly. /In many in- 

 stances, indeed, quite new types of life^eem to come 

 suddenly into existence, but wherever this is the 

 case we find that there is usually a break in our 

 record of history*. Now if we take into account the 

 long periods of "'unrecorded history that intervened 



