SUB-CLASSES OF BIRDS. 229 



strong rtiddei'-feathers in twos, so that the whole tail 

 appears regularly feathered. This same formation of the 

 tail part of the vertebral column occurs transiently in the 

 embryos of other birds, so that the tail of the Archseopteryx 

 evidently represents the original form of bird-tail inherited 

 from reptiles. Large numbers of similar birds with lizard- 

 tails probably lived during the middle of the secondary 

 period ; accident has as yet, however, only revealed this one 

 fossil. 



The Fan-tailed, or Keel-breasted birds (Carinatse), which 

 form the second sub-class, comprise all living Birds of the 

 present day, with the exception of those of the ostrich 

 kind, or'Ratitte. They probably developed out of Feather- 

 tailed Birds during the first half of the secondary period, 

 namely, in the Jura or chalk period, by the hinder tail 

 vertebrae growing together, and by the tail becoming 

 shortened Only very few remains of them are known 

 from the secondary period, and these moreover only out of 

 the last section of it, namely, from the Chalk. These remains 

 belong to a swimming bii'd of the albatross species, and a 

 wading bird like a snipe. All the other fossil remains of 

 birds as yet known have been found in the tertiary 

 strata. 



The Bushy-tailed, or Ostrich-like Birds (Ratitse), also 

 called Running Birds (Cursores), the third and last sub- 

 class, is now represented only by a few living species, by 

 the African ostrich with two toes, the American and 

 Australian ostrich with three toes, by the Indian cassowary 

 and the four-toed kiwi, or Apteryx, in New Zealand. 

 The extinct giant birds of Madagascar (yEpyomis) and the 

 New Zealand Dinornis, which were much larger than the 



