XXX IXTRODUCTION, 



living. In rocks of more recent date, the orders 

 and families correspond to those at present 

 existing, though the genera and species still 

 remain dissimilar. Grradually, even these ap- 

 proximate ; first the genera, and, finally, the 

 Rpecies becoming identical with those of the 

 present da}^ 



XOTES. 



T. In the 'Principles of Psychology,' by Herbert Spencer, 

 various definitions of Life are discussed. 



2. Aristotle — m^, lumv Tivio-ioj;. 



3. Owen — ' Lectures on the Comparative Anatomy and Physio- 

 logy of the Invertebrate Animals.' 



4. See Huxley — ' On the Method of Paleontology,' (in Annals 

 of Natural History, 1856.) 



5. Huxley — 'Report upon the Researches of Professor Miiller 

 into the Anatomy and Development of the Echinoderms,' (in Annals 

 of Natural History, 1851.) 



6. Von Baer — 'Ueber Entwickelungs-geschichte der Thiere.' 

 See also Carpenter — ' Principles of Comparative Physiology.' 



7. CuviER, in a Paper read before the French Academy, first 

 clearly announced the existence of distinct plans of structure in the 

 Animal Kingdom. See his ' Regne Animal,' 2^^ edition. 



8. Huxley — ' Lectures on General Natural History,' published in 

 the Medical Times and Gazette. 



9. J. Mt'LLER — ' Handbuch der Physiologic des Menschen.' 



10. J. D. Hooker and T. Thompson — ' Introductory Essay to 

 the Flora Indica.' 



1 1. See Lyell — ' Principles of Geology ;' and Forbes — ' On the 

 Connection between the Distribution of the existing Fauna and Flora 

 of the British Isles, and the Geological Changes vrhkh have affected 

 their Area,' &c. (in the Memoirs of the Geological Survey of Great 

 Britain, 1846.) 



