6 BIOLOGICAL SOCIETY OF WASHINGTON. 



The fact that these portions of matter are organic, in no re 

 spect releases them from the common servitude of matter to 

 the laws of mechanics through the operation of physical 

 forces. 



If then development of structure is constrained to operate 

 within a limited field, which can hardly be denied, all those 

 calculations based upon the assumption that the field is unlim 

 ited fall to the ground and may be safely disregarded as 

 irrelevant. 



The operations of biologic selection may be divided into two 

 categories, ist. these in which fitness and unfitness are deter 

 mined by the perfection in adjustment of the individual to the 

 mechanics of the environment, which will include the great 

 mass of the lower organisms ; and 2nd., those in which intelli 

 gence becomes a factor. The latter will include all forms of 

 sexual selection, mimicry, protective coloration, and every 

 case in which discrimination on the part of pursuer or pursued 

 may come into play. It is by no means necessary that the or 

 ganism which becomes modified should possess even conscious 

 ness, but one of the two parties to the modification, at least, 

 must possess intelligence of a certain grade. The mental 

 qualities of the insect are necessary to the modification of the 

 colors of the orchid, as far as they serve to attract its attention 

 or direct its movements, while the modifications of the stigma 

 or pollen mass to facilitate cross fertilization, fall into the other 

 category. 



While the operations of the first category must always have 

 been active, and probably were not supplemented b}^ those of 

 the second category for an immense period of time, yet I be 

 lieve the latter also to be very ancient. - It is probable, how 

 ever, that influences of the second category operate more 

 rapidly and are productive of much greater diversity in devel- 



