THE GREAT FISH-LIZARDS. 43 
and the hinder or pelvic pair no doubt were of great service 
in helping the creatures to come up to the surface when 
necessary. 
Thus we see that the whale, with its one pair of paddles, has a tail 
specially planned with a view to rapid vertical movement through 
the water ; while in the fish-lizards, who did not require to breathe 
so frequently, the tail-fin was planned with a view to swift and 
straight movement forward as they pursued their prey, and they 
were compensated by having bestowed upon them an extra pair 
A B € 
Fic. 4.—(A) Lateral and (B) profile views of a tooth of J/chthyosaurus 
platyodon (Conybeare), Lower Lias, Lyme Regis, Dorsetshire. (Cc) Tooth of 
Ichihyosaurus communis (Conybeare), Lower Lias, Lyme Regis, Dorset. 
of paddles. Thus we learn how one part of an animal is related 
to and dependent upon another, and how they all work together 
with the greatest harmony for certain definite purposes (see 
p.'@): 
These great marine predaceous reptiles literally swarmed in 
the seas of the Lias period, and no doubt devoured immense 
