20 



i.u/;/.'/r.i.\ Mrsj':cM of xatium. history 



was rciiiarkahlc tni- the cliscoN-crics 

 ill all hraiu'hos of natural science. 

 \)v Hlainvillc (1S39-1S49) and Lycll 

 (1797-1875) made valuable contribu- 

 tions to ])ahe()nt()l()<;y and «>;e()lof»;y. 

 J.yeirs "Pnncii)les of (;eol()<:;y" (1S:^)()- 

 IS:^:^) dealt a death blow to catastro- 

 ])hisni. and is a work ('(jual in inipoi't- 

 ance in its own field to the "()ri,«!;in 

 of »S])ecies" in biolo*;^ . 



:\lilne-E(hvard8 (1800-1818) enun- 

 ciated the ])rincii)le of th(^ i)hysiolo^ical 

 division of lal)or. \'on Baer (1828) 

 announced the law that bears his name, 

 namely, ^ 'individual development is a 

 recapitulation of race development." 

 Sehleiden and Schwann (1838-1839) 

 described cells in plants and animals, 

 and propounded the cell theor}-. 

 Valentin (1839) named the ' 'nucleus," 

 and was the first to speak of the ' 'cell 

 theory." Purkinje and von Mohl 

 (1840) named the living substance 

 of the cell protoplasm, sl term in 

 universal use to-day. De Barry 

 (1843) observed the union of sperm 

 and ovum. Kolhker (1846) demon- 

 strated that spermatozoa develop in 

 the tissues of the testes. Owen (1840) 

 point(Hl out the difference between 

 hot)wlo(jous organs, for example, the 

 arm of man, fore limb of horse, and 

 win"- of bird, orj>;ans which are formed 

 on the same structural i)lan. and 

 analogous organs, for examj^le, wing 

 of l)ir(l and wing of butterfly, organs 

 diffcM'ing entirely in structure, ])ut 

 jK^rforming tlu^ same function. 



l{emak (1850) described "three 

 germinal layers," and Huxley (1859) 

 homologized them in the lower animals. 



Rapid strides were made also in 

 systematic zoology and in zoo- geogra- 

 phy. The relations of the lower 

 animals wvvv worked out by Lcnickart, 



X'aughn, Thompson. Dujardin, Agassiz 

 and a host of others. 



I^xj)editions were sent out to explore 

 the earth and the sea. Famous among 

 these are the voyage of the ''Beagle," 

 on which Darwin served and did some 

 of his earliest biological work; and 

 the voyage of the "Rattlesnake," on 

 \\hi('li Huxley was Assistant Surgeon. 



In 1859 Darwin i)ublished his 

 "Origin of Species," a book which is 

 universall\* a'dmitted to have had 

 more influence on human thought 

 than any other work of the century. 



Darwin's theory of the "Origin of 

 Species" may be stated briefly as fol- 

 lows: All species tend to vary. Xo 

 two individuals of the off.spring of a 

 pair are exactly alike. On account 

 of this variation in structure or func- 

 tion, certain individuals are better 

 able to thrive than their fellows. 

 These animals transmit these charac- 

 ters to their offspring, which in turn 

 survive in the struggle with their fel- 

 lows. Thus nature eliminates those 

 variations which are disadvantageous 

 to the organism, each individual being 

 tested in its struggle to maintain its 

 existence. The accumulation of these 

 favorable variations through many 

 generations is supposed to prockice 

 an organism quite dift'erent from the 

 original stock, or, in other words, a 

 new form. 



Few works have l^een constructed 

 with more care and skill. For more 

 than twenty years Darwin collected 

 facts from all available sources, and 

 made innumerable observations him- 

 self. The evidence in support of 

 his tluH)ry was dra^^^l from many 

 branches of natural science: compara- 

 tive anatomy-, embryolog>^ paUeon- 

 tology and zoo-geography. So num- 



