1 32 NATURE STUDIES. 



and ifc may thus represent that stage in the evolution 

 of the bird-type wherein the type of limb common to 

 the primitive stock. was being gradually modified into- 

 the more consolidated limb of the bird. 



Thus to-day, there exists a series of forms, detached 

 and isolated, perhaps, but still eloquent enough in 

 their declaration of the existence in past epochs of" 

 animals which belong to no one class as defined by us- 

 to-day, and which further stand intermediate between 

 existent classes of living beings. The existence of 

 these "links," to argue backwards, is inexplicable,, 

 save on the theory of evolution, or 011 that of the 

 production of ' ' freaks " by nature ; and this last idea, 

 I apprehend, is put out of court, by every considera- 

 tion worthy the name of scientific thought. 



PART IV. THE LOWEST QUADRUPEDS. 



The quadrupeds l or Mammals, as they are techni- 

 cally called form an important group of animals, not 

 merely because in structure they represent the per- 

 fection of the animal world, but because they stand at 

 the head of the animal creation, apparently separate 

 and distinct from all other and lower classes. The 



1 A correspondent, " J. Fisher, M.D.," in a letter addressed to 

 the Editor of Knowledge, remarks that the names " Quadrupeds " 

 and " Mammals," used by me as synonymous terms (and, I may 

 add, in strict accordance with natural history usage), are apt to 

 convey what he is pleased to call an " erroneous impression." He 

 remarks that the whale is a " Mammal," but not a " Quadruped ' 

 meaning, of course, that a whale has not four legs. Dr. Fisher 



