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COLLEGE ZOOLOGY 



Figure 461, Jean Baptiste Lamarck (1744-1829), 

 the French biologist who developed a theory of 

 organic evolution based largely on the inheritance 

 of acquired traits. Although there is no good evi- 

 dence of the inheritance of acquired characters, yet 

 nearly every generation sees a revival of it in one 

 form or another. 



Karl Ernst von Baer (1792-1876), a Rus- 

 sian zoologist, developed the science of com- 

 parative embryology. His investigations on 

 the cleavage of the egg, the germ layers, 

 and the differentiation of tissues led to the 

 formulation of the germ-layer theory and 

 the recapitulation theory. 



Charles Darwin (1809-1882) (Fig. 462) 

 inaugurated a new era in zoology by publi- 

 cation in 1859 of a book entitled The Origin 

 of Species by Aleans of Natural Selection. 

 Natural selection as a factor in organic 

 evolution has already been noted. Danvin 

 spent 20 years accumulating facts which 

 seemed to substantiate his theory and then 

 gave to the world a book that was over- 

 whelming in its effects. Advances in our 

 knowledge, especially in the field of genetics, 

 have necessitated modifications of Darwin's 

 ideas, but no other publication ever exerted 

 as great an influence on biology as did his 

 epoch-making book. Belief was prevalent at 



Figure 462. Charles Darwin (1809-1882), the 

 English zoologist who wrote The Origin of Species 

 by Means of Natural Selection. This photograph 

 was taken at the age of 72. He is wearing the black 

 hat and cloak used for walks in his garden at Down 

 House, the quiet country place near London where 

 he lived most of his adult life. Down House is now 

 a national memorial under the auspices of the British 

 Association. (Courtesy of Underwood and Under- 

 wood. ) 



that time in the inheritance of certain types 

 of variations that are now known not to be 

 passed on to offspring. The modern view of 

 how organic evolution has taken place we 

 owe to the geneticists. 



Gregor Mendel (1822-1884) (Fig. 463) 

 initiated modern methods of studying gene- 

 tics. He was a monk in an Augustinian 

 monastery in what was then Briinn, Austria, 

 but is now Brno, Czechoslovakia. His experi- 

 ments were carried on in the cloister garden 

 (Fig. 407). He worked principally with 

 garden peas, from which he derived the first 

 scientific expression of the laws of heredity. 

 His results, which were published in 1866, 



