ON THE HYPOTHESIS OF EYOLUTIOK 141 



the still more ancient Cretaceous periods, living at the present 

 day.* That this discovery invalidates in any wise the conclusions 

 of geology respecting lapse of time is an unwarranted assumption 

 that some are forward to make. If it changes the views of some 

 respecting the parallelism or co-existence of faunas in different 

 regions of the earth, it is only the anti-developmentalists whose 

 position must be changed. 



For, if we find distinct geologic faunae, or epochs defined by 

 faunae, co-existing during the present period, and fading or merg- 

 ing into one another as they do at their geographical boundaries, 

 it is proof positive that the geologic epochs and periods of past 

 ages had in like manner no trenchant boundaries, but also passed 

 the one into the other. The assumption that the apparent inter- 

 ruptions are the result of transfer of life rather than destruction, 

 or of want of opportunities of preservation, is no doubt the true 



one. 



8. Rationale of Development. 



a. In Characters of Higher Groups. — It is evident in the case 

 of the species in which there is an irregularity in the time of com- 

 pletion of metamorphosis, that some individuals traverse a longer 

 developmental line than those which remain more or less incom- 

 plete. As both accomplish growth in the same length of time, it 

 is obvious that it proceeds with greater rapidity in one sense in 

 that which accomplishes most ; its growth is said to be accelerated. 

 This phenomenon is especially common among insects, where the 

 females of perfect males are sometimes larvae or nearly so, or pupae, 

 or lack wings or some character of final development. Quite as 

 frequently, some males assume characters in advance of others, 

 sometimes in connection with a peculiar geographical range. 



In cases of exact parallelism we reasonably suppose the cause 

 to be the same, since the conditions are identical, as has been 

 shown ; that is, the higher conditions have been produced by a 

 crowding back of the earlier characters and an acceleration of 

 growth, so that a given succession in order of advance has extended 

 over a longer range of growth than its predecessor in the same al- 

 lotted time. That allotted time is the period before maturity and 

 reproduction, and it is evident that as fast as modifications or 

 characters should be assumed sufficiently in advance of that pe- 

 riod, so certainly would they be conferred upon the offspring by 



* Most of the deep-sea forms are, however, degenerate forms of existing orders. 

 (Ed. 1886.) 



