HISTORT OF ZOOLOGY. 15 



of fishes; similar organs may also undergo a change of function 

 from one group to another; the hydrostatic a^jparatus of fishes has 

 come to be the seat of respiration in the mammals. Organs with 

 like functions — physiologically equivalent organs — are called 

 'analogous'; organs of like anatomical constitution — anatomically 

 equivalent organs — are called ' homologous. ' It is the task of 

 comparative anatomy to discover in the various parts of animals 

 those which are homologous, i.e. those anatomically equivalent, 

 and to follow the changes in them conditioned by a change of 

 function. 



Cuvier. — The foremost rejiresentative of comparative anatomy 

 was Georges Dagobert Cuvier. He was born in 1769 in the town 

 of Mompelgardt (Montbeillard), then belonging to Wiirtemberg, 

 and obtained his early training in the Karlschule at Stuttgart, 

 where, through the influence of his teacher Kielmeyer, he was led 

 to the study of comparative anatomy. The opportunity of going 

 to the seashore which was oft'ered to him as j^rivate instructor to 

 Count d'Hericy he employed for his epoch-making investigations 

 upon the structure of molluscs. In 1794, ujion the persuasion 

 largely of the man who afterwards became his great ojDjjonent, 

 Geoffroy St. Hilaire, he moved to Paris, where he was made at 

 first Professor of Xatural History in the central school and in the 

 College of France, later Professor of Comparative Anatomy in the 

 Jardin des Plantes. As a sign of the great regard in which Cuvier 

 was held, it should be noticed that he was repeatedly intrusted with 

 high educational positions and was made a French peer. As such 

 he died in 1832. 



Type Theory. — Cuvier's investigations, apart from the mol- 

 luscs, extended to the crelenterates, arthropods, and vertebrates, 

 living and fossil. He collected his extensive observations into his 

 two chief works " Le regne animal distribue d'apres son organiza- 

 tion '" and " Lec;ons d'anatomie comparee." Of quite epoch-making 

 importance was his little pamphlet " Sur un ra^jprochement a etablir 

 entre les differentes classes des animaux," in which he founded his 

 celebrated type theory, and which in 1813 introduced a complete 

 reform of classification. The Cuvierian division, which has become 

 the starting-point for all later classifications, differed, broadly 

 speaking, from all the earlier systems in this, that the classes of 

 mammals, birds, reptiles, and fishes were brought together into a 

 higher grade under the name, introduced by Lamarck, of ' verte- 

 brate animals'; that further the so-called ' invertebrate animals ' 

 were divided into three similar grades, each equal to that of the 



