INCREASE IN NUMBER OF KNOWN SPECIES. 15 



much to say that not a day passes without adding new 

 species to our lists. A comparison, for instance, of the 

 edition of Cuvier's ' Regne Animal/ published in 1828, 

 as compared with the present state of our knowledge, 

 is most striking. 



Dr. Giinther has been good enough to make a calcu- 

 lation for me. The numbers, of course, are only ap- 

 proximate, but it appears that while the total number 

 of animals described up to 1831 was not more than 

 70,000, the number now is at least 320,000. 



Lastly, to show how large a field still remains for 

 exploration, I may add that Mr. Waterhouse estimates 

 that our Museums contain not fewer than 12,000 species 

 of insects which have not yet been described, while 

 our collections do not probably contain anything like 

 one-half of those actually in existence. Further than 

 this, the anatomy and habits even of those which 

 have been described offer an inexhaustible field for 

 research, and it is not going too far to say that there 

 is not a single species which would not amply repay 

 the devotion of a lifetime. 



One remarkable feature in the modern progress of 

 biological science has been the application of improved 

 methods of observation and experiment ; and the em- 

 ployment in physiological research of the exact mea- 

 surements employed by the experimental physicist. Our 

 microscopes have been greatly improved : achromatic 

 object-glasses were introduced by Lister in 1829 ; the 

 binocular arrangement by Wenham in 1856 ; while 

 immersion lenses, first suggested by Amici, and since 

 carried out under the formula of Abbe, are most valuable. 

 The use of chemical re- agents in microscopical investiga- 



