636 HISTORY OF SCIENCE. 



ideas which originated, or, at least, were first clearly enunciated, by 

 a few philosophers about the close of last and beginning of the present 

 century. Some of these ideas have been placed before the reader in 

 Chapter XV. (page 390), where Lamarck's "Philosophic Zoologique" 

 is referred to in connection with our notice of that author and his 

 classification of the invertebrata. ETIENNE GEOFFROY ST. HILAIRE 

 (17721844), another great French naturalist, who has also been 

 referred to in Chapter XV., had by the close of last century put for- 

 ward on the transformation of species views essentially the same as 

 those of Lamarck. But whereas the latter considered that the use or 

 disuse of organs was the agency of the transformation, St. Hilaire 

 conceived it to be effected rather by changes in the surrounding cir- 

 cumstances ; as, for example, when he thinks that birds may have 

 originated from lizard-like reptiles by a diminution of the carbonic 

 acid in the atmosphere, in consequence of which a more active oxy- 

 genation and higher temperature of the blood quickened the creatures 

 and caused their scales to become feathers, etc. St. Hilaire main- 

 tained that throughout the animal world there existed a general plan 

 of organization, the mere modification of which in this or that direc- 

 tion gave rise to the different races of animals. This unity of plan or 

 homology may be illustrated by the identity of structure which is found 

 beneath the superficial differences in the arm of a man, the fore-leg 

 of a horse, the wing of a bird, and the paddle of a whale. In the 

 earlier part of the century commenced many warm controversies on 

 such topics, and we find Cuvier opposing the homological views of 

 St. Hilaire with all his might. In the year 1830 a debate was carried 

 on between these two naturalists on the unity of animal organization 

 before the Academic des Sciences, and was continued for five sittings. 

 An account of this debate, with remarks upon the points raised, was 

 the very last production of the great German poet GOETHE (1750 

 1832), written but a few months before his death. Goethe had in 

 the course of his life devoted not a little attention to science, and 

 written on such subjects as osteology, meteorology, geology, etc. 

 Perhaps but for his unfortunate theory of colours the ideas Goethe 

 had himself put forth on certain points of natural history would sooner 

 have commanded attention, as they tended powerfully to support the 

 notion of the unity of organic nature. The existence of an inter- 

 maxillary jaw-bone in the human subject was one of Goethe's own 

 discoveries, inferred from the law of homology, and confirmed by 

 actual observation after the examination of a great number of human 

 skulls. 



There is another kind of homology to which Goethe was one of the 

 first to draw attention as a law of animal organization. It is the re- 

 lation of similarity in the parts placed one behind another in the same 

 individual. An instance so familiar as to be recognized by every 

 one is the similarity of the legs and arms. The correspondences of 



