252 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



To sum up, it will be seen that the epochs of 

 appearance of each great group of fossil animals 

 even of those highest in the zoological scale go 

 further and further back into time as palaeontological 

 discoveries accumulate. We have long known 

 that in the Cambrian epoch most of the great 

 groups of the Invertebrates were already sharply 

 distinct, and that, consequently, we must almost 

 give up the hope of one day discovering the primi- 

 tive types of the Foraminifera, the Sponges, the 

 Corals, the Cystoidea, the Crinoids, the Brachio- 

 pods, the Lamellibranchs, the Gastropods, the 

 Cephalopods, the Trilobites, the Meros tomes, and 

 even, no doubt, the air-breathing Articulates. It 

 is probable that in a few years we shall have to say 

 the same of the great classes of the Vertebrates, 

 since already we are certain that the Fishes go 

 back at least to the Ordovician, the Amphibians to 

 the Devonian, the Reptiles to the Carboniferous, 

 and the Mammals to the Trias. If there has really 

 been, as is probable, a gradual improvement in 

 the organic world, and if the animal types are the 

 more recent as their organization is higher, we 

 shall certainly be called upon to push back for 

 several geological periods all the dates which mark 

 provisionally the inception of all our branches. 



