THE PROGRESS OF LIFE 87 



F. Osborn, however, includes many of these in the 

 primitive Insectivora, thus classing them with the 

 Eutherian mammals. All these Marsupials belong to 

 the section called Polyprotodonta, with numerous 

 small, sub-equal, incisor teeth, and are allied to the 

 opossums, bandicoots, and native cats of Australia. 



CAINOZOIC LIFE 



In comparison with the fauna, the flora of the 

 Cainozoic era is very imperfectly known, owing to 

 the difficulty of distinguishing plants by their leaves 

 only ; while their classification depends chiefly on 

 their flowers, of which very few have been preserved 

 as fossils. In the Eocene period the land was either 

 covered with forests, or else by wide stretches of 

 brown ferns, except in the swamps, where rushes and 

 other herbaceous monocotyledons grew. Probably 

 there were no herbaceous dicotyledons until the 

 upper Eocene. Before then the land must have 

 looked much like the north island of New Zealand at 

 the present day, where it is untouched by civilised men ; 

 and but few butterflies and bees could have existed. 



The dicotyledons are usually dividedinto three groups : 



(1) The Apetalse, in which the perianth consists 



of the calyx only. 



(2) The Polypetalse, which has a corolla formed 



by four or five separate petals, in addition 

 to the calyx. 



(3) The Gamopetalas, in which the lower portions 



of the petals are united together to form a 

 tube, which protects the honey secreted at 

 its base. 



