( Ixxxii ) 



viduals can be expected to be influenced by external conditions 

 in precisely the same way, there would at first arise a fluc- 

 tuating and undirected variability, representing physiological 

 modifications, of which some would be better adapted to the 

 changed conditions than others. Those individuals whose 

 physiological processes were best suited to the new conditions 

 would survive and gradually supplant the less suited indi- 

 viduals in the usual way. This might be called natural 

 physiological selection. With this change there would occur 

 a simultaneous change of external correlates — the outward 

 manifestation of the internal readjustment ; the undirected 

 variability would become more definite, and, finally, the 

 species would become transformed by a process which at first 

 sight might appear to be simply climatic, but which in reality 

 would have been brought about by the displacement of the 

 physiologically unfit. Or, again, a species might experience 

 periodic climatic change in its own region, and require periodic 

 physiological readjustment. Of all the functions of an organ- 

 ism, those classed as physiological are probably the most 

 elastic — the most susceptible of meeting new conditions. In 

 insects undergoing complete metamorphosis, the pupal period 

 of histolysis and histogenesis is no doubt as critical physio- 

 logically as it is morphologically. But an exaggerated 

 physiological elasticity is required to meet some kinds of 

 periodic change, such as that of the seasons, and it is worth 

 considering the whole phenomenon of seasonal dimorphism 

 from this point of view. Is it not that the two seasonal forms 

 represent dift'erent physiological forms, the special activities 

 being adjusted to ditt'erences of temperature, amount of 

 moisture, etc. ? May it not be that the selection of individual 

 physiological adaptability has brought about this result ? If 

 these questions can be answered in the affirmative, then the 

 experiments of Dorfmeister, Weismann, Edwards, Merrifield, 

 Fischer, Standfuss, and others, simply mean that these 

 observers have produced, by the action of temperature, an 

 efi'ect upon pup* which by natural selection have been 

 rendered adaptable* to changes of temperature, and that the 



* This remark, of course, only applies to species which have become 

 seasonally dimorphic, and of such spacies only to those in which the two 



