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, wh.il e 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) w,as 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 



