Revieics — Prof. A. Gaudry — On Evolution. 39 



magne and the age of Louis Quatorze, so may we speak of the age 

 of Paradoxides, the age of Slivionia, the age of Pterichthjs, the age 

 of Coccostem, of Megalichthys, of Euchirnsam-us. 



" Frequently, those organisms which have been the most specialized 

 and most perfect of their genus have the soonest died out. Para- 

 doxides, Slimonia, Pterichtkys, have mai'ked the culminating point of 

 divergence which their type was to attain. They could therefore no 

 longer produce new forms ; and as the normal characteristic of 

 creatures is either to change or die, — they died. Alongside these 

 transition forms, offering these eccentric variations, there have been 

 others, whose individuality has been less pronounced, being of inter- 

 mediate position, representing in the animal kingdom the juste milieu. 

 Amongst these we find the types which have been more persistent, 

 just as in our day we find cosmopolitan forms, which are found in 

 all parts of the world, so there have been forms which one might call 

 panchronic, for they have been of all epochs. 



" They have constituted a sort of permanent reservoir from which 

 have arisen at every moment in geological time beings destined to 

 take a more or less high position. 



"It might perhaps be possible that the shorter lives of those genera, 

 which in their own classes show the highest perfection, may have 

 sometimes had its cause in this same perfection. The greater the 

 complexity of an organism, the less chance is there of the modification 

 of one of its parts ; consequently, it must suffer more from changes 

 in its surrounding circumstances, and must make a more delicate 

 subdivision in the changes which mark geological time. The power 

 of longevity resides partly in their plasticity ; they recall the fable 

 of the oak and the reed. Like the reed, these weakly creatures have 

 bowed before the storms of time, and have thus been preserved, 

 whilst the giants of the organic world fell. We must, moreover, 

 confess that we can but very imperfectly explain this inequality of 

 the evolution of animals ; for we see in one and the same class, and 

 at the same epoch, beings which are at different stages of develop- 

 ment ; for example, I have already mentioned that in the Permian 

 formation of Igornay we find together Actinodon, of which the verte- 

 br£e still retain their centra unossified (notochordal), and StereoracJns, 

 in which the centra are fully ossified. 



" Brachiopoda offer us singular inequalities in the persistence of 

 genera. The Lingidce, the CranicB, and the RhyncJwnellai have con- 

 tinued throughout all subsequent geological times without any 

 notable change ; whilst Pentamerus, and Producta, and many other 

 genera have not survived the Primary epoch. 



" We find together with types absolutely special to Primary times, 

 tj'pes closely related to our Nautili and Limidi which have had the 

 singular destiny of being spectators of all the changes of the organic 

 world from the days of the Trilobites to our own times. 



" The difficulty which we find in understanding the causes of the 

 evolution of ancient organisms is no reason for denying this evolu- 

 tion ; for the embryogenical metamorphisms which we witness 

 every day are in no wise less unequal than the palseontological ones. 



