NATURAL SCIENCE IN THE NINETEENTH CENTURY 393 



. .To these ideas Lamarck clung in spite of criticism, for in the 

 Introduction to his Natural History of Invertebrates, a much later 

 work than his Zoological Philosophy, he again affirms : 



I conceive that a gasteropod mollusk [e.g. a snail], which, as it 

 crawls along, finds the need of touching the bodies in front of it, 

 makes efforts to touch those bodies with some of the foremost parts 

 of its head, and sends to these every time quantities of nervous fluids 

 as well as other liquids. I conceive, I say, that it must result from this 

 reiterated afflux towards the points in question that the nerves which 

 abut at these points will by slow degrees be extended. Now, as in 

 the same circumstances, other fluids of the animal flow also to the 

 same places, and especially nourishing fluids, it must follow that 

 two or more tentacles will appear and develop insensibly in those 

 circumstances at the points referred to. 



The principal significance of these views to-day is in the attempt 

 which they embody to explain on natural principles phenomena 

 then explained only as supernatural. 



VOYAGES AND EXPLORATIONS OF NATURALISTS. In the nine- 

 teenth century voyages, expeditions, and explorations for the first 

 time were undertaken for the sole and specific purpose of the 

 improvement of natural knowledge (to use a phrase associated with 

 the origin of the Royal Society). Of these the first were those of 

 Alexander von Humboldt who, beginning in 1799, made numerous 

 and extensive journeys and observations by land and sea which 

 enabled him many years later to publish his monumental Kosmos, 

 a work replete with observations and reflections on natural phi- 

 losophy and natural history, which eventually gave him a place, in 

 this century, among the learned men of Germany second only to 

 that occupied by Goethe. 



In 1801, Robert Brown, a British botanist, worthy of remem- 

 brance also in connection with the so-called Brownian movement 

 of particles under the microscope, accompanied an expedition 

 to Australia and brought back representatives of some 4000 new 

 species of plants. Most fruitful of all was Darwin's famous voy- 

 age of the Beagle to the Pacific (1831-1836), while in 1838 

 Karl Ernst von Baer, the eminent founder of comparative embry- 



