478 
Among the Amphibia the Apoda, or limbless Amphibia, give 
an example of homoplasmy. Writing of these, Gadow remarks 
that : 
‘“About forty species are known, these have been placed in seventeen 
genera, mostly on comparatively slight grounds, and several of these genera 
are probably unnatural, the distinctive characters having undoubtedly been 
developed independently in various countries.’ ** 
Among the lizards we find five families without limbs which 
have evidently lost them quite independently of one another. 
The burrowing snakes have a number of characters in common, 
but they have more than one origin. 
According to many authorities, the birds are not descend- 
ants of the Dinosaurs, in spite of the many characters common 
to both. However striking these characters are, “they are in- 
stances of convergent analogies, the upright walk, which has 
been assumed and improved upon independently by members of 
both Theropoda and Orthopoda, has produced the same, or 
nearly the same modifications in them as in birds.” * 
Among the mammals we find the Metatheria or Marsupials 
and the Eutheria developing along independent lines, but reach- 
ing a number of very similar results. As an example, I quote 
the Marsupial mole (Notoryctes) and the Eutherian mole 
(Talpa) and its allies. 
The Cetacea or whales, the Sirenia and the Carnivora Pinni- 
pedia have traveled along the same lines of development inde- 
pendently, and the fossil reptile /chthyosaurus has also traveled 
along the same lines, which is similar to the normal form of 
fishes, and apparently is the best adapted to life in the water. 
In these cases there are innumerable characters in morphology 
and anatomy which had to be modified to convert these land, 
or at most amphibious, animals into complete or nearly com- 
plete aquatic animals. Some birds have also taken to aquatic 
life and have been independently modified along lines to fit them 
for that element. Many insects belonging to different families 
have also been modified along lines adapting them for a life in 
the water. 

** Camb. Nat. Hist. VIII, Amphibia and Reptiles, p. 89 (1901). 
* Gadow, Camb. Nat. Hist. VIII, p. 416 (1901). 
