40 BIOLOGICAL SOCIETY OF WASHINGTON. 



not onlv from the current crude popular conception of it, but 

 also from the ideas which prevail among well informed and 

 even scientific persons. I need not, I am sure, apologize in 

 this age of specialists, for having confined myself almost ex- 

 clusively to that kingdom of life with which I am most 

 familiar. I believe that I can safely assume that the zoologists 

 present, in whatever branch, have been able to parallel all the 

 illustrations which I have given by similar ones in their own 

 •departments, leading to the same general conclusion. 



EXTRA NORMAL DEVELOPMENT. 



Thus far I have only taken account of what may be called 

 the normal or legitimate causes of siich advantageous modifica- 

 tions of structure as have resulted in the successive upward 

 steps which organic life has taken in the course of its history. 

 But there is another class which may be called extra-normal, 

 abnormal, or even illegitimate causes. Normal or legitimate 

 causes are such as result in the production of characters which 

 are of direct use to the organism. In extra-normal or illegiti- 

 mate causes the characters produced are such as have only an 

 indirect effect. Thus in the vegetable kingdom normal devel- 

 opment tends chiefly in the direction of strengthening the 

 stem, increasing the foliar surface, and protecting the germ and 

 reproductive organs, i. c, in the direction of strength, nutri- 

 tion, and reproduction, these being the three prime essentials 

 of existence. The various modes of strengthening the trunk r 

 and especially the attainment of complete exogeny, as seen in 

 the trees of the present day, directly improved the conditions 

 of existence and the chances for further development. The 

 gradual attainment of broad appendicular expansions called 

 leaves increased more and more the power to decompose the 



