272 TOWARDS THE HUMAN FORM 



open out their wings as they fell, in order to start flying again. 

 The size of Pteranodon indicates that insects must have in- 

 creased greatly during the Cretaceous Period. The existence of 

 Dimorphodon in the Lias proves that numerous flying Insects 

 must have already existed. But we have still to discover what 

 use Ramphorhyncus and the Pterodactyls made of their 

 teeth, which were too long for such minute prey. This seems to 

 imply that Birds already existed, and that Archceopteryx 

 was perhaps not the most perfect of them. 



We come at last to those Reptiles which invaded the water 

 during the Secondary Period. This return to a former environ- 

 ment need not unduly astonish us, since Crocodiles have never 

 abandoned the neighbourhood of rivers. Since the time of the 

 Trias there had been marine Reptiles whose legs, by a contrary 

 process from that which took place in Dinosaurians, were 

 shortened and broadened. The digital phalanges were often 

 multiplied and the feet finally transformed into paddles which 

 could only have been used for swimming. They belonged to two 

 types : in one, the Plesiosaurians, also called Hydrosaurians or 

 Sauropterygians, the head was small and the neck elongated, 

 as in the Dinosaurs, but the tail was very short ; in the other, 

 that of the Ichthyosaurians or Ichthyopterygians, the head, 

 on the contrary, was large, the neck very short, the tail long but 

 flattened, which, like a fish's tail, gave the animal the greatest 

 possible impetus in swimming. To these differences in aspect 

 two quite different modes of life must have corresponded. 

 The Plesiosaurians, swimming only by means of their lateral 

 paddles, helped perhaps by the undulations of their long, 

 swan-like necks, probably lived on the surface, and must 

 have been able to dive quite easily, but confined themselves 

 to shallow waters, where they probed and dug the mud in 

 the manner of geese and swans. The Ichthyosaurians, on the 

 contrary, lived like real Fishes, and only came to the surface 

 in order to breathe, as our Porpoises do. Swimming not 

 only with their paddles but also by the aid of their tails, the}' 

 would be met with the same resistance by the water as are 

 Fishes. Hence their neck would be shortened and they would 

 acquire the same shape as the Fishes. In the fine 

 palaeontological gallery of the Paris Museum, there may be 

 seen an example, acquired by the Societe des Amis du Museum, 

 preserved with its integument held together by small scales. 



