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met with, and it is only in the groups of the Mam- 

 mals and perhaps of the Reptiles that it becomes 

 possible to present a few examples sufficiently de- 

 monstrative. Thus the Eocene, Oligocene, and also 

 in part the Miocene Mammals may be looked upon 

 up to a certain point as early forms of the existing 

 types. There can be determined, in most orders of 

 mammals, a certain number of primitive charac- 

 teristics which correspond to various adolescent 

 stages in the existing representatives of these 

 groups. On the other hand, these early mammals 

 are deprived of some of the most remarkable pe- 

 culiarities of the present types, such as the horns 

 and their bony antlers, the welding together of 

 certain bones, and the reduction in the number of 

 the teeth and some portions of the skeleton. It is 

 thus possible, by studying carefully a series of the 

 kindred genera of different geological ages, to see 

 appear, one after another, in the series of time, the 

 characteristics of differentiation and of progressive 

 specialization of the modern types. 



But this is only a very fragile and very uncertain 

 basis for the reconstruction of the faunas and floras 

 of the past. Experience has taught us to what 

 uncertainties and to what errors the study of palse- 

 ontological facts by the method of embryology 

 might lead us. Let us imagine a zoologist who 

 would wish to attempt the reconstruction of the 

 series of ancestors of the Crinoids by means of the 

 ontogeny of the Antedon. The lowest types of his 

 pedigree would have to possess a stalk with a cup 

 without handles, formed of five basal and five oral 

 pieces close together ; then would come genera in 



