The Story of Evolution 97 



mammals as well. These higher Vertebrates are therefore called 

 Amniota in contrast to the Lower Vertebrates or Anamnia (the 

 Amphibians, Fishes, and primitive types). 



It is a suggestive fact that the embryos of all reptiles, birds, 

 and mammals show gill-clefts a tell-tale evidence of their dis- 

 tant aquatic ancestry. But these embryonic gill-clefts are not 

 used for respiration and show no trace of gills except in a few 

 embryonic reptiles and birds where their dwindled vestiges have 

 been recently discovered. As to the gill-clefts, they are of no 

 use in higher Vertebrates except that the first becomes the 

 Eustachian tube leading from the ear-passage to the back of the 

 mouth. The reason why they persist when only one is of any Use, 

 and that in a transformed guise, would be difficult to interpret 

 except in terms of the Evolution theory. They illustrate the 

 lingering influence of a long pedigree, the living hand of the past, 

 the tendency that individual development has to recapitulate 

 racial evolution. In a condensed and telescoped manner, of 

 course, for what took the race a million years may be recapitu- 

 lated by the individual in a week ! 



In the Permian period the warm moist climate of most of 

 the Carboniferous period was replaced by severe conditions, cul- 

 minating in an Ice Age which spread from the Southern Hemi- 

 sphere throughout the world. With this was associated a waning 

 of the Carboniferous flora, and the appearance of a new one, con- 

 sisting of ferns, conifers, ginkgos, and cycads, which persisted 

 until near the end of the Mesozoic era. The Permian Ice Age 

 lasted for millions of years, and was most severe in the Far South. 

 Of course, it was a very different world then, for North Europe 

 was joined to North America, Africa to South America, and 

 Australia to Asia. It was probably during the Permian Ice Age 

 that many of the insects divided their life-history into two main 

 chapters the feeding, growing, moulting, immature, larval 

 stages, e.g. caterpillars, and the more ascetic, non-growing, non- 

 moulting, winged phase, adapted for reproduction. Between 



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