532 POPULAR SCIENCE MONTHLY, 



belonged to genera wliicli exist in our seas such as Lingula, 

 Rhynclionella, and Terebratula. Besides fishes of special types, 

 "we find some with tendencies toward those of to-day. Prof. Vail- 

 lant, examining a Permian genus which I had described under 

 the name of MegopleuTon, thought it was so nearly like some liv- 

 ing ceratodes of Australia that he proposed to describe it under 

 the same generic name. The Primary reptiles, although very 

 different from those of our epoch, have many characters of re- 

 semblance to them. For example, having occasion to study in 

 detail the reptiles of the Permian, I was very much struck by 

 seeing that their heads had the same bones, both above and 

 below, as in the existing animals. MM. Marcellin, Boule, and 

 Glangeaud, comparing the paws of a reptile of the same forma- 

 tion with those of a common varanus, remarked their extreme 

 similitude. 



When we come to the Secondary formations, we find many 

 invertebrate animals related to living genera. Most of the ver- 

 tebrate animals are easily distinguished from present genera, 

 though usually not because they present any unknown special 

 features, but because they combine characteristics that are now 

 distributed among distinct classes. M. Seeley has recently de- 

 scribed Triassic quadrupeds from Africa which diminish the dis- 

 tance between the reptiles and the mammals ; the icthyosaurus, 

 which is cited as one of the most extraordinary fossils, recalls the 

 fish in its vertebrae, the massive mammals in its fore flippers, and 

 the reptiles in its other characteristics. Although the pterodac- 

 tyl certainly belongs to the class of reptiles, its manner of flying 

 is like that of flying mammals. The iguanodon is a reptile with 

 its hinder limbs forerunners of those of birds. On the other 

 hand, the archseopteryx is a bird with reptilian recollections. 

 The Secondary fossils, which have surprised paleontologists so 

 much by their singular features, in reality establish connections 

 among animated beings instead of disclosing gaps. 



In the Tertiary epoch the existing genera rhinoceros, tapir, 

 boar, gazelle, elephant, hyena, cat, bear, etc. appear each in its 

 turn. We find species, as well as genera, so near living forms 

 that it is difficult not to suppose their near relationship. 



Finally, the species of Quaternary times are for the most part 

 identical with those of to-day, or so little different that they may 

 be considered simply as races. It is impossible to mark a bound- 

 ary between beings that existed before us and those that live 

 with us. 



It must therefore be recognized that the fossil world is not 

 distinct from the existing world; there is only a single world, 

 which has continued from the most ancient ages till our days. It 

 can be studied as if it were an individual ; in the same way as we 



