THE HISTORY OF ZOOLO 



509 



efficient agents in the modification of species. Wallace, how- 

 ever, has always adhered to his original theory, and is I 

 one of the firmest advocates of the complete sufficiency of natural 

 selection. 



To scientists in general, Darwin's theory of natural selection 

 came as something entirely new, but it had actually been sug- 

 gested by two writers earlier in the century, although neither 

 of them appreciated its full significance. The Englishman, 

 Wells, read a paper before a scientific societv in 1813, in which 

 lie recognized the principle of natural selection as applying to 

 human races; this paper was published in [818. Another 

 British writer, Matthew, published a work in 1 831, in which 

 he formulated briefly a theory of evolution based on the princi- 

 ple of natural selection. But although Darwin was not the first 

 to discover this principle, his conception of it was original ; he 

 was entirely unaware of the works of the earlier writers. Very 

 many writers have dealt with this subject since the publication 

 of the " Origin of Species " ; the two whose works have had the 

 widest interest probably are the German, Haeckel (1834-), whose 

 theoretical writings have been criticised chiefly for their incon- 

 sistencies, and his fellow-countryman, Wei s man n ( 1834- ), whose 

 contribution to the theory we have already noted. In England, 

 Huxley (1825-1895) has been one of the most ardent writers on 

 evolution, and has in addition made important contributions to 

 anatomy. 



W T e have already remarked that the first half of the nineteenth 

 century was especially noteworthy for the great advances made 

 in anatomical knowledge ; in a similar way the second half was 

 characterized by a truly marvelous increase of embryological 

 knowledge. Much of this was doubtless due to the great per- 

 fection brought about in the construction of the compound 

 microscope during this period, and the improved technique em- 

 ployed in preparing objects for microscopic study. Combinatit »ns 

 of lenses are now made which give a magnification of 3000 

 diameters; there are drawbacks to the use of such high powers, 

 however, and for ordinary work it is not necessary to use a 

 magnification greater than about 1000 diameters. By further me- 

 chanical devices it is now possible to cut delicate objects into 

 sections a thousandth of a millimeter thick, which thus become 



