43 
Of course other vertebrates produce venom. An American lizard, Heloderma 
suspectum, has a venomous bite, and the male Platypus has poisonous spurs on 
the hind feet, but venom is of less importance in creatures that have limbs to 
hold struggling prey and, apart from Snakes, it is a rarity. 
Now, for completeness, we must turn to the remaining two groups of Verte- 
brates — Birds and Mammals. In Birds, none have been found that have survived 
loss of both hind limbs, though small birds, as individuals, can survive quite well 
the accidental loss of one leg and, in the Swifts, the legs are reduced to the point 
where take-off from level ground is impossible. But quite a lot of birds have lost 
or degenerated fore-limbs, wings, to the degree that flight is impossible. 
A primitive toothed sea-bird, whose fossils have been found in cretaceous 
deposits, appears to have entirely lost its wings. It is no more. The Great Auk 
and the Dodo both survived for some time loss of adequate wings, but they too 
have succumbed to competition from more active creatures. Penguins have lost 
flight, but their wings remain adequate as flippers for swimming, and they have 
survived successfully by confining their life to the sea, and to lands whose island 
smallness or whose severe Antarctic climate have preserved them from active land 
predators. 
The main group of birds in which the fore-limbs, wings, are almost or 
entirely lost, is the Ratitae, the Ostrich and its kin. Most of this group, which lost 
flight very early in the bird evolution, have survived by virtue of mutations which 
have given them powerful legs. The Ostrich can run as fast almost as any 
mammalian carnivore, and its kick has been favourably compared to that of a 
mule. The Emu and Cassowary can also give a good account of themselves;. I have 
never heard of the South American Rhea's powers of self-defence but they, also, 
are good runners and large carnivores are uncommon on the Pampas, where 
Rheas live. Probably the chief enemy of the Ratitae is man, who almost certainly 
killed off the Aepyornis in Madagascar and the Moa in New Zealand. 
Generally speaking, loss of fore-limbs in birds is an unfavourable mutation 
which cannot be fully compensated, and leads slowly to extinction wherever there 
is competition from carnivorous quadrupeds, let alone man. 
Lastly Mammals. Two groups have lost hind limbs, the Whales and the Sea- 
cows or Syrenia. Both of these groups appear to have lost the legs after returning 
to life in water. In the sea, a stream-lined body, with a tail-fin to give a grip on 
the water, is more important than limbs. In fact, limbs adapted for swift running 
are a positive hindrance. The Syrenia have been adapted to aquatic life by 
acquisition of a flattened tail and flippered arms, but otherwise by little change. 
The group has spread widely geographically, but has not diversified. A point 
which may be significant is that the group is herbivorous while most other verte- 
brates which have lost limbs are carnivores. Steller's Sea Cow is recently extinct; 
Dugongs and Manatees appear to be on the way out. 
The Whales are often divided into two Orders, the Toothed Whales and the 
Whalebone Whales, but I shall consider them together. The wide radiation of 
form in the group, shows it to be a much more successful type and they have 
survived by a number of favourable mutations. The fore-lirnbs have become 
flippers and a wide tail-fin has developed. This, like the smaller tail-fin of 
Syrenia, is horizontal instead of vertical, which shows it to be a completely fresh 
mutation and unrelated to the vertical tail-fin of Fishes and the vertical narrowing 
of the tail of Sea-snakes. A thick coat of blubber aids streamlining and protects 
from the cold of the sea. Internal developments have occurred which save the 
Whales from getting the "bends" when they surface from a deep dive. We are 
still uncertain about these, but they may be connected with a big blood volume 
and, of course, whales can hold their breath for a long period and do not, cannot, 
breathe air at high pressure under water, as a human diver must do. Toothed 
whales have been able to revert to the peg type of tooth which seems most useful 
to most underwater feeders, and mutations have given the Whalebone Whales a 
filter for extracting plankton from the water which is very efficient. 
But perhaps the most important mutations are those associated with the 
central nervous system. We know that Dolphins have a system of sonar location, 
at least as good as that of bats, and they have a brain equal to making full use 
of this. The small Whales — Dolphins have been studied particulary — have large 
brains in relation to their body size, and in complexity are comparable to those 
of men. They are probably the animals next to man in mental ability, more 
