NATURAL SELECTION. 
155 
naturally supposed to be distinct kinds of Batrachians; but 
the experiments of Prof. Marsh anc 
eom 
| Prof. Dumeril have 
demonstrated that changing the conditions of existence 
has the effect of metamorphosing the Siredon into an 
Amblystoma. The importance of these experiments may 
be appreciated by supposing that Tadpoles reproduced 
Tadpoles in Nebraska or Mexico, and Frogs reproduced 
Frogs in New Haven or Paris, and that anatomists regarded 
the Tadpole as an entirely distinct Batrachian from the Frog ; 
but removing the Tadpoles to New Haven or Paris, and 
changing the conditions of existence, the Tadpole turned 
into a Frog: our hypothetical case is exactly that of the 
Siredon and Amblystoma. As Professors Marsh and Du- 
meril developed a lung-breather, the Amblystoma, from a 
gill-breather, the Siredon, so we believe nature to have 
developed the lung-breathing Frogs from gill-breathing 
tadpole-like animals. Thus, in remote time, the condi- 
tions of existence changing, some of these tadpole-like 
animals changed into Frogs, while others remained un- 
modified and reproduced tadpole-like animals. But as the 
development of the individual Frog is the epitomized history 
of the race to which it belongs, the developing Tadpole, 
or the transitional stages of the Frog, are permanently 
represented by animals like the Salamander and Proteus. 
An important consequence of the Struggle for Existence 
is the Division of Labor so characteristic of man, the 
higher animals, and plants. Savages supporting them- 
selves by hunting and fishing, while often acting in concert, 
are, however, not dependent upon one another, so that the 
sudden death of even many individuals does not cause any 
inconvenience to the rest of the tribe. But in the civilized 
state, where the crowding together of people diminishes the 
means of subsistence and increases the number of rivals, 
the Struggle for Existence soon differentiates the population 
into growers of corn, hewers of wood, and carriers of water, 
