Revieivs — Prof. A. Gaudry — On Ecohttion. 35 



Coelenterata, Echinodermata, Molliisca, and Crustacea, In the Silurian 

 there are Echini, Crinoids, Starfish, which appear to be as distinct 

 from each other as these groups are at the present day." 



" I confess," says Prof. Gaudry, " when I began to study the 

 Eeptiles of the Permian, which in certain respects present characters 

 of inferiority, I expected to find relations between them and the 

 fishes ; but I found, on the contrary, that these early reptilia, by the 

 full development of their fore and hind limbs, as well as by their 

 thoracic and pelvic girdles, were as different as possible from the 

 class of Fishes. These facts, which set forth clearly the sepai-ation 

 of the principal classes of the animal world in very remote times, 

 need not, I think, astonish zoologists. The more accomplished 

 observers refuse to admit a single linear series, commencing at 

 the Monad and continuing step by step, through the Polype, the 

 Echinoderm, the Mollusc, the Worm, the Articulata, the Fish, the 

 Eeptile, the Bird, the Mammal, and ending at Man. 



"Although the Mammalia are the most perfect of the Vertebrata, 

 the study of their embryological development does not show that 

 they have passed througli the fish and the bird-stage. Palgeon- 

 tologists are in accord with embryologists, when they see that in 

 geological times there has not been one single line of connexion, 

 but many lines of relationships, the development of which has been 

 pursued independently. 



" In whatever manner we may suppose that evolution was pro- 

 duced, it seems most probable that it was marked by successive 

 progress in the course of geological epochs. We are ignorant as 

 to what occurred before the Cambrian epoch ; but since then the 

 history of living beings has been marked by progress. In Silurian 

 times the animals have become more numerous and more varied 

 than in the Cambrian epoch. The Coelenterata, the Echinodermata 

 and the Cephalopoda, here take an extension previously unknown. 

 Beside the Trilobites are seen the Merostomata, and the end of the 

 Silurian epoch even witnesses some fishes. But in all the earlier 

 half of this immense epoch we have neither fishes nor Merostomata. 

 The sovereigns of ocean were no other than the Trilobites and the 

 Cephalopods. 



" The animals met with in the primary formations are for the 

 most part, and notably in the Silurian, seen to have been better 

 organized for defence than for attack, as though in the earlier days 

 of the globe, the animals being fewer, the means of preservation was 

 more necessary. 



" Thus certain Eugosa had opercula, the Cystideans were enclosed 

 in calcareous tests, and even the greater part of the Criuoids, 

 properly so-called, instead of having their viscera unprotected, like 

 the Secondary forms, had them enclosed in a case which recalls the 

 arrangement in the Cystidea : Brachiopoda could onl}' slightly open 

 their valves : Maclurea and several Pteropods had opercula. 



"Amongst the Cephalopoda the aperture was often contracted.' I 



1 Many of the Ammonites were furnished with a shelly QT^erc\A\\m. {=Aptijchis, 

 Triyoneliites, etc.,- homologous with the dorsal hood of NautUus) closing the aperture 

 of their body-chamber.— Edit. Geol. Mag. 



