92 



THE DATA OF BIOLOGY. 



the fire. But in these cases, we do not see a connexion 

 between the changes undergone and the preservation of the 

 things that undergo them; or, to avoid any teleological im- 

 plication the changes have no apparent relations to future 

 events which are sure or likely to take place. In vital 

 changes, however, such relations are manifest. Light being 

 necessary to vegetal life, we see in the action of a plant 

 which, when much shaded, grows towards the unshaded side, 

 an appropriateness which we should not see did it grow 

 otherwise. Evidently the proceedings of a spider which 

 rushes out when its web is gently shaken and stays within 

 when the shaking is violent, conduce better to the obtain- 

 ment of food and the avoidance of danger than were they 

 reversed. The fact that we feel surprise when, as in the case 

 of a bird fascinated by a snake, the conduct tends towards 

 self-destruction, at once shows how generally we have observed 

 an adaptation of living changes to changes in surrounding 

 circumstances. 



A kindred truth, rendered so familiar by infinite repetition 

 that we forget its significance, must be named. There is 

 invariably, and necessarily, a conformity between the vital 

 functions of any organism and the conditions in which it is 

 placed between the processes going on inside of it and the 

 processes going on outside of it. We know that a fish can- 

 not live long in air, or a man under water. An oak growing 

 in the ocean and a seaweed on the top of a hill, are incredible 

 combinations of ideas. We find that each kind of animal is 

 limited to a certain range of climate ; each kind of plant to 

 certain zones of latitude and elevation. Of the marine flora 

 and fauna, each species is found only between such and such 

 depths. Some blind creatures flourish in dark caves; the 

 limpet where it is alternately covered and uncovered by the 

 tide; the red-snow alga rarely elsewhere than in the arctic 

 regions or among alpine peaks. 



Grouping together the cases first named, in which a parti- 

 cular change in the circumstances of an organism is followed 



