Memoires de la Societe d'Hist. Nat. de Paris. 537 



shell is merely the vitellum of the egg. We therefore repeat, 

 that individuals must be bred by some able naturalist, that 

 their daily developement must be observed, that the eggs must be 

 watched until the animals have attained their full growth, and 

 that until this has been eifected, doubts will still continue to 

 exist. 



The remaining articles connected with Zoology which are con- 

 tained in this volume, are chiefly geological, the references to the 

 animal kingdom, being, with one exception, almost entirely inci- 

 dental. In the " Geological Description of the Tertiary Basin 

 of the South-west of France, by M. B. de Basterot," the author 

 gives the characters, descriptions, and synonyms, of three hun- 

 dred and thirty species of fossil shells collected in the neigh- 

 bourhood of Bourdeaux, many of which are figured in the accom- 

 panying plates. Although many of them are new, they present 

 too little which is of general interest to induce us to enter into 

 particulars with respect to them. We shall therefore limit our 

 notice of this article to a single observation advanced in it, which 

 is equally applicable to the Zoology of the present age, and of 

 past ages. 



It may be affirmed, says M. de Basterot, that no species of 

 MoUusca, whether inhabiting the land or the water, is to be 

 found perfectly identical in two or more situations, which are 

 considerably distant from each other, or in which there exists 

 a difference in the nature of the soil or of the waters. A little 

 more or less of elongation in all the parts, of prominence in the 

 striae and in the tubercles, of thickness in the folds, &c. is al- 

 ways to be met with, and the determination of species is thus 

 rendered a very difficult task. In the examination of a long 

 series of species from dilTerent localities, there appears to be a 

 kind of succession of undulations around certain determinate 

 forms, extending so far that the extremes of one are con- 

 founded with those of another, the centres still remaining perfectly 

 distinct. The great extent of these variations, is readily to be 

 accounted for on the principle of Cuvier, that the differences 

 which constitute varieties depend on determinate circumstances, 

 and that their developement increases, in proportion to the intcu- 



