276 GENERALIZATIONS. 



some of their genera in Tertiary strata are now extinct. With 

 reference to another class of animals, the insect fauna of the 

 Tertiary epoch differs more than the molluscan fauna from 

 the living races of the present day ; but among Miocene insects 

 the cockroaches, grasshoppers, and Termites, which must be re- 

 garded as most ancient types, in some cases approach very nearly 

 to existing forms. 



The flora and fauna of the present day represent the most 

 highly organized forms. Consequently in approaching a more 

 perfect state of the vegetable and animal kingdoms, an advance 

 in the organization of living creatures took place, and a definite 

 progress may be traced in their development. In the most 

 ancient periods we know only cellular Cryptogams (p. 233) ; in 

 the Carboniferous epoch the vascular Cryptogams predominate, 

 and from the Trias to the Chalk the Gymnosperms * ( Conifers 

 and Cycads) . The Dicotyledonous flowering plants (leafy trees 

 and shrubs) make their first appearance in the Cretaceous epoch, 

 and only acquire their full development in the Tertiary period ; 

 and from that time they constitute the great mass of the flora. 

 But in Tertiary periods the apetalous and lowest forms take the 

 first rank, and the monopetalous types, which occupy the highest 

 grades in the vegetable kingdom, only attain their fullest deve- 

 lopment in the existing creation. There is therefore unmis- 

 takably, on the whole, a progressive development from the more 

 simply constructed towards the more complicated and conse- 

 quently more highly organized types. And the same pheno- 

 menon is met with in the animal world. Palaeozoic rocks offer 

 us Zoophytes, Mollusca, Annulosa, and Vertebrata, or represen- 

 tatives of the four great main divisions of animals; but of the 

 last there is only the lowest class, Fishes, and these are repre- 

 sented by peculiar forms indicative of a very inferior grade of 



* Formerly Conifers and Cycads were united with Dicotyledons, but they 

 are most nearly related to the vascular Cryptogams, and form the transition 

 from the flowerless to the flowering plants, as is proved by the admirable in- 

 vestigations of Hoffmeister on the structure of their flowers and ovules. 

 Their woody structure, also, is simpler than that of the Dicotyledons, as it 

 consists of uniform cellls ; and their pits, which were formerly regarded by 

 some as of a glandular nature, cannot be taken as indications of higher 

 organization. 



