MOTIVE. 



The prescient glimpse of the principle "I'Unite de Composition Or- 

 ganique " in the Animal Kingdom, which gnided the labours of Geoffrey 

 St.-Hilaire, and was propounded in his first contribution* to a ' Phi- 

 losophic anatomique,' called forth the comments of his ablest contem- 

 poraries. Of these the article by Plourensf discusses the subject in 

 relation to the Vertebrate type. Geoffrey's subsequent volume illustrative 

 of his ruling idea by the phenomena of " Monstruosities " was the subject 

 of a similar favourable analysis by Frederic CuvierJ. 



To the difficulties which the Invertebrates seemed to Duges to oppose 

 to an acceptance of Geoffrey's generalization he replied §, by reference 

 to " fig. 2 de la septieme planche : — La se trouve effectivement represente 

 un homard couche sur le dos et montrant distinctivement ses visceres dans 

 la position oil le sent les visceres des mammiferes places sur le ventre "||. 



Hereupon Baron Cuvier intervened, with the object set forth and 

 illustrated in his notable paper in the ' Annales des Sciences I^aturelles,' 

 referred to in the first of the following essays. 



This phase of the discussion, which I was favoured, in 1831, to hear 

 in the Hall of the Institute allotted to the Academie des Sciences, has 

 seldom since been absent from my thoughts in connexion with any obser- 

 vations and researches which seemed to throw light upon it. The 

 exposition of the nature of the structures which Cuvier deemed fatal to 

 Geoffrey's illustration of his principle is the chief subject of the two 

 following essays. 



* " Des organes respiratoires, sous la rapport de la determination etde I'identite de 

 leurs pieces osseuses." 



t ' Analyse de la Philosopbie anatomique,' 8vo, 1819. 

 I In 'La Eevue encyclopedique,' torn. xvii. Fevrier 1823. 

 § In the Part " Sur la Vertebre," 1822. 



|j " Lettre sur quelques points du Memoire ayant pour titre : De la Oonformite or- 

 ganique dans rEchelle animale/' in ' Gazette Medicale de Paris,' No. 44, 1831, p. 4. 



