THE SCIENCE OF BIOLOGY 423 



discovered microscopic animals, spermatozoa, and other structures, 

 they were unwittingly pioneering in the field of Cellular Biology. 



Biology in the Eighteenth Century. The next great ad- 

 vance in the science dates from 1735, when Linnxus, a Swede, first 

 published his Sy sterna Naturce, a work that brought order out of 

 disorder in the attempts to arrange animals and plants according to 

 various schemes of classification. The methodical mind of Linnaeus 

 established a rational basis for grouping plants and animals; his sys- 

 tem is the basis of modern Taxonomy (p. 95). With this reason- 

 able arrangement of plants and animals according to their struc- 

 tural similarities and dissimilarities as the basis for study, the 

 conditions were established for the revival of the Greek concept of 

 evolution, inactive since the days of John Milton and Suarez (p. 

 389). Linnaeus himself regarded species as fixed and without the 

 possibility of change, but the constant studies that his system of 

 classification provoked of structural similarities in time could not 

 fail to bring to recognition by others of the fact that such similarities 

 represent actual relationships. Hence in the latter part of the eight- 

 eenth century Buflfon, a Frenchman, and Erasmus Darwin, an Eng- 

 lishman, advanced their incomplete theories of evolution (p. 389) 

 and in the first years of the nineteenth century the fully formed 

 theory of Lamarck came forth. Charles Darwin's additions to the 

 doctrine date from 1859, and the stimulus given by Darwin's great 

 work still carries on. 



The Cell Doctrine. Protoplasm. Meanwhile observers with 

 the microscope had improved their instruments and had collected 

 facts. In 1838 Schleiden, a Dutch botanist, and Schwann, a Dutch 

 zoologist, together arrived at the important generalization that the 

 cell is a structural feature common to all living objects and that it 

 is the ultimate living unit. There followed a period of contention 

 over the relative importance of the cell wall and the cell contents, 

 until 1 861, when the German, Max Schultze, in a masterly analysis 

 of the facts then at hand promulgated the protoplasm doctrine and 



