42 The Ma/{e-Up and the Workings of the Earth 



group. One must conclude that the modern Paludina is 

 descended from forms represented by the fossils, and that 

 through the ages there has been modification along with the 

 continuity of life, even though we may not be able to guess 

 what brought the changes about. 



Another remarkable series of snails has been worked up 

 from Wurttemberg. Here there is not only a progressive 

 change from the ancient type to the modern, but repeated 

 divergence resulting in several distinct types that even an 

 untrained eye can readily separate. There are evidences here, 

 in other words, of an ancient ancestor with several distinct 

 types of descendant. Similar series of sea urchins have been 

 worked out from the chalks of England. 



Evolution of Mammals 



More interesting to most of us are the recent additions 

 to our knowledge of ancient life which link up familiar ani- 

 mals like the horse, the elephant, and the camel with their 

 respective ancestors. 



The family to which the horse belongs (the Equidas) is 

 represented by fossils of the Eocene period, of little hoofed 

 animals having five toes, and not at all resembling the modern 

 horse in outward appearance, the Eohipptis. Fossils found 

 in Europe and North America supply a remarkably complete 

 series connecting these animals with the modern horse 

 (Fig. 8) . There is a progressive reduction in the number of 

 toes while the middle toe becomes larger. There is a lengthen- 

 ing of the legs. There is a lengthening of the neck and of 

 the head. There are progressive changes in the teeth. And 

 there is a progressive increase in body size. 



Out of materials assembled from Egypt, North America, 

 India and Europe, a fossil series showing the ancestral his- 

 tory of the elephant has been built up (Fig. 9) . The fossils 

 from the Eocene of northern Egypt represent an animal 

 about three feet tall resembling the modern tapir. Fossils 

 from the Oligocene period, found in India as well as in Egypt, 



