THE STUDY OF BIOLOGY. 23 



private life for a while, and indicates that it possesses not merely a 

 nervous apparatus analogous to our own, but that such apparatus is 

 used in an exactly similar fashion. A broad likeness exists between 

 a snail's retirement into its shell when touched, and the human act 

 of withdrawing the head from a threatened blow. And so we find 

 that from the animalcule to man, from the lowest plant to the highest 

 member of the vegetable kingdom, there exist means whereby the 

 living being, through the property of sensitiveness or " irritability " (as 

 we may term the general function of nervous tissue or its represen- 

 tative), is brought into relation with its surroundings. This act of 

 relating itself to the outer world in which it lives, constitutes the 

 third function of life wherever found. The nerve-acts whereby man 

 is enabled to think, feel, and move; the actions whereby a daisy 

 closes its florets when the chill of evening falls upon the world ; the 

 act of a Venus's fly-trap or a sundew in capturing the insects on 

 which, like vegetable spiders, these plants feed ; and the humbler 

 manifestations of sensation seen in the sluggish movement of an 

 animalcule or in the cells of a seaweed are bound together in one 

 harmonious function, which we name that of Relation, Innervation, 

 or Irritability. To nourish itself, to reproduce its kind, and to 

 maintain relations with the world in which it lives such is the whole 

 physiological duty of man and animalcule alike ; and in the survey 

 of these three functions is comprehended the answer to our second 

 question, " How does the animal or plant live ? " 



The third inquiry of the biologist, as we have seen, relates to the 

 place and position of the living being on the surface of the world 

 whether it be found on the earth itself or in the waters under the 

 earth, whence by deep-sea research the knowledge of its habitat has 

 been drawn. Every animal and every plant, besides a name and 

 designation, possesses a " local habitation " on the earth's surface. 

 The study of structure and the knowledge afforded by physiology 

 take no account of the dwelling-places of animals and plants. 

 " Where is it found?" is thus a question which must also be asked of 

 the biologist ; and for the answer we depend upon a third branch of 

 biology, to which the name of Distribution has been given. 



The purport of the inquiry, " Where is it found ? " requires no 

 explanation. The most natural of queries concerning a living being 

 is that which the child might ask concerning the native habitation of 

 an animal or pknt Outward nature appeals too forcibly to us to 

 render the question, " Where does it come from ? " an unnatural one 

 when applied to the animal or plant ; the difference between our own 

 land and habitation and those of other men being included in some 

 such interrogation as that involved in the questions which the science 

 of Distribution professes to answer. No more interesting queries 

 can well be imagined within the whole range of natural-history study 



