408 TUE PR INC IPLES OF SCIENCE. 



pagated itself almost from primeval times with little vari 

 ation. 



In other cases frequent differentiations will have oc 

 curred. Strictly speaking, this genealogical tree ought to 

 represent the descent of each individual living form now 

 existing or which has existed. It should be as personal 

 and minute in its detail of relations, as the Stemma of the 

 Kings of England. We must not assume that any two 

 forms are absolutely and exactly alike, and in any case 

 they are numerically distinct. Every parent then must 

 be represented at the apex of a series of divergent lines, 

 representing the generation of so many children. Any 

 complete and perfect system of classification must regard 

 individuals as the infimae species. But as in the lower 

 races of animals and plants the differences between indi 

 viduals are usually very slight, and apparently unimportant, 

 while the numbers of such individuals are immensely great, 

 beyond all possibility of separate treatment, scientific men 

 have always stopped at some convenient but arbitrary 

 point, and have assumed that forms so closely resembling 

 each other as to present no constant difference were all of 

 one kind. They have, in short, fixed their attention 

 entirely upon the main features of family difference. In 

 the genealogical tree which they have been unconsciously 

 aiming to construct, diverging lines meant races diverging 

 in character, and the purpose of all efforts at so-called 

 natural classification was to trace out the relationships 

 between existing plants or animals. Now it is evident 

 that hereditary descent may have in different cases pro 

 duced very different results as regards the problem of 

 classification. In some cases the differentiation of charac 

 ters may have been very frequent, and specimens of all 

 the characters produced may have been transmitted to the 

 present time. A living form will then have, as it were, 

 an almost infinite number of cousins of various degrees, 



