248 NATURAL SCIENCE. Oct., 



him, have been led aside by the very natural claim upon the atten- 

 tion which the results of variation must present. We have in nature 

 thousands of species and varieties living lives as diverse as are their 

 bodily constructions. These are the objects of interest to the 

 naturalist, and the chief aim of his study is to discover how they 

 arose and what was the story of their development. But we have to 

 remember that, although to us variations are of great interest, they 

 but occasionally establish and transmit themselves — one to a million 

 as against the transmission of more typical individuals. 



For a thousand years the bird which has white plumage or the 

 sheep which has short legs will die of hunger or fall a prey to foes 

 before even sexual maturity is reached. Only when it finds itself in 

 a land of snow will the white bird have a chance, and the sheep with 

 short legs is only safe when taken under the protection of the farmer. 

 But this establishment of a variation is not an everyday circumstance 

 in the life of a species, it occurs only now and then : for a hundred to 

 one, a thousand to one, or even a million to one, the best thing is to be 

 typical of the species, to be a conservative, a true chip of the old 

 block. Many species, like the housefly and cockroach, have come 

 down to us practically unaltered since geological times, and the 

 changes occurring in most species only occur with extreme slowness. 



Living forms are, therefore, not only capable of variation, but by 

 sexual conjugation these variations tend, as it were, continually to be 

 brought back into the fold. By sexual conjugation we have the 

 possibility of the long continuance of a type when it has adapted 

 itself fully to its environment ; by variation we have a means of adap- 

 tation to a new or changing environment. Were it not for conjugation 

 we should not iind living forms existing in genera and species. With 

 asexual reproduction we should have an infinite number of varieties, 

 each of these giving rise, in course of time, to new ones. With con- 

 jugation we have the inter-action of individuals upon one another, 

 with the formation of progeny which, on the whole, tends to a mean ; 

 and among individuals capable of thus conjugating, the resemblance 

 between them is maintained, and they form a group recognisable by 

 common characters. 



I am convinced by many personal conversations that the facts 

 relating to chemical combinations have greatly influenced the minds 

 of biologists, and have led them to accept increased variation as the 

 rule of conjugation. The facts of chemistry are better established 

 and more easily understood than the facts with which we have to 

 deal ; and not unnaturally we frequently turn to them and try to 

 arrange and interpret our facts by the side of these. Much good may 

 come of this method provided we remember that living matter exhibits 

 phenomena which non-living matter does not, for a phenomenon in 

 chemistry may sometimes lead to the discovery of a similar one in biology 

 by setting us to look for it. We have, however, no warrant for assuming 

 that we shall find all chemical phenomena repeated in biology. No 



