PHENOMENA OF REGRESSION AND CONVERGENCE 223 



examples most often quoted is the convergence of 

 the Secondary Marine Reptiles of the order of the Ich- 

 thyosaurs with the Tertiary and existing Dolphins. 

 The general form of the body, the long snout fur- 

 nished with conical teeth, the very short neck, the 

 transformation of the fore limb into a natatory 

 paddle, cause between the Ichthyosaurs and the 

 Dolphins great analogies in appearance and in 

 biological character, striking enough to have fos- 

 tered the hypothesis of an ancestral parentage ; 

 but they cannot stand against an examination of 

 the structure as a whole. Similarly neither the con- 

 vergence of some characteristics between the Flying 

 Reptiles or Pterosaurians and the Birds, nor the 

 presence of a horny bill in the genus Pteranodon, the 

 birdlike head placed at right angles on a long and 

 strong neck, and the pneumatic nature of the bones 

 can prevent, notwithstanding the authority of 

 Seeley, our recognizing the essentially Reptilian 

 characters of the Pterodactyls. I i 



A mode of convergence rather more embarrassing 

 at least as far as outward appearance goes is 

 furnished by that tendency to excessive elonga- 

 tion of the body with a more or less complete dis- 

 appearance of the limbs, which leads to the type 

 called anguilliform or serpentiform, according to 

 whether it refers to aquatic or terrestrial Vertebrates. 

 Several very different families of the lower Verte- 

 brates exhibit this type of structure. The Dolicho- 

 soma of the Carboniferous epoch among the Stegoce- 

 phalic Amphibians, the Eel and many other genera 

 among Fishes, the Ceciliae among existing Batra- 

 chians, the Amphisbaenas among the Lacertians, 



