284 
ORIGIN OF LIFE IN AMERICA 
zuela within comparatively recent geological times, a con¬ 
clusion which perfectly agrees with the results obtained from 
other faunistic evidence. 
The groups of smaller mammals which have representa¬ 
tives in the West Indies are the rice-rats (Oryzomys) and 
the musk-bearing rats (Moschophoromys =Megalomys). Like 
the hutias and solenodons, the latter are confined to this 
region, but they are only known from the Lesser Antilles, 
Moschophoromys desmaresti being peculiar to Martinique, 
whereas M. luciae is only found on St. Lucia. The occurrence 
of this peculiar genus of small mammals on the Lesser 
Antilles implies that their connection with the mainland must 
be of longer standing than is generally supposed. The 
opossum (Didelphys marsupialis), is one of the few species 
of terrestrial mammals having a wide range in both North 
and South America, and must, therefore, be considered as 
a persistent specific type of great antiquity. It may possibly 
have retained its specific characters, while the ancestors of 
the musk-bearing rats rapidly became modified on the islands. 
That the latter are not recent introductions is likewise in¬ 
dicated by the fact that an extinct species of Moschophoromys 
is known from Barbados. 
The rice-rats (Oryzomys) inhabit both the islands and the 
mainland. Their very wide and discontinuous range in North 
and South America at once suggests an ancient origin. One 
species (0. antillarum) was so abundant in Jamaica, and did 
such damage to the crops, that the mongoose, a small carni¬ 
vore, was imported from India for its destruction. For a 
time the experiment appeared to be quite successful. After 
some ten years, however, when the rice-rats became scarce, 
the mongoose began to pay attention to snakes, lizards, 
tortoises and birds. As it developed a taste for them they 
in their turn became scarce, until it was found that 
the mongoose was worse than any other animal pest, for, 
owing to the great destruction of the useful members of 
the fauna, insects and ticks had increased to an alarming 
extent. The disturbance of the due balance of nature by 
man is always risky, and thus sometimes leads to incalculable 
damage. 
A second species of rice-rat (0. victus) is peculiar to the 
