THE MIDDLE PAST. 



MESOZOIC SYSTEMS THE TRIAS, OOLITE, AND CHALK. 



WE now take leave of the palaeozoic aspects of the world, 

 and pass on to those of the Mesozoic or "middle life" 

 period characterised by forms and species which hold an 

 intermediate place between those of the more ancient and 

 those of the more modern epochs. The grand primeval 

 types and patterns are still the same radiate, niolluscan, 

 articulate, and vertebrate but the modifications of the types 

 are new, and the consequent organisation higher and more 

 complex. The " differentiation" of the vital functions (as 

 zoologists express it) now becomes more marked and ap- 

 parent that is, instead of organisations in which several 

 functions are performed by the same organ, each function 

 has an organ specially devoted to its purpose. The expres- 

 sion of Creative thought has become more specialised, and 

 the plants and animals of the newer epochs bear the im- 

 press of that specialisation, and find in new external condi- 

 tions a fitting habitat for their growth and elimination. 



We noAV take farewell of the graptolites, cystideans, tri- 

 lobites, and eurypterites of Silurian seas of the gigantic 

 crustaceans and bone-cased fishes of the old red sandstone 

 of the sigillarire, stigmariae, lepidodendra, and other endo- 

 genous forms of the coal period of the cup-in-cup, honey- 



