THE MIGRATIONS OF MARINE ANIMALS 281 



animals correlative to great changes in the palceo- 

 geography of continents was fully recognized a 

 century ago by G. Cuvier. The illustrious founder 

 of palaeontology was struck with good reason by the 

 absence or rarity of forms of transition between 

 superposed fossil faunas. Exaggerating, no doubt 

 for want of documentary evidence, the consequences 

 of this observed fact, Cuvier concluded that an 

 integral renewal of faunas had taken place, % not 

 by successive creations, *as he has often been wrongly 

 reported to have said, but by distant migrations 

 of animals foreign to the region. Later, numerous 

 palaeontologists, Darwin, Wallace, Lydekker, Zittel, 

 Schlosser, Gaudry,Dollo, Osborn, Matthew, Ameghino, 

 and Deperet with regard to the terrestrial Verte- 

 brates, Pictet, Desor, Fischer, Tournouer, Wood, 

 Murray, Dolfus, Fontannes, Van den Broeck, etc., in 

 the case of the Invertebrates, have directed their 

 researches to these phenomena and have made their 

 bearing apparent. Though the observations in this 

 respect still present numerous gaps and include 

 a good many rather hypothetical data, the results 

 obtained up till now none the less offer the greatest 

 interest and deserve all our attention. 



In a very general way, it may be affirmed that 

 the evolution of a group has hardly ever been 

 effected on one and the same spot on this globe. 

 Nearly always the successive representatives of a 

 branch endowed with any considerable longevity 

 have emigrated several times in the course of their 

 history, becoming extinct in one region, to carry on 

 in another and more or less distant one a new 

 phase of their morphological destiny. The evolu- 



