3i7 
Another cause of extinction is to be found in the sudden 
invasion of a particular area by an animal which is the foe 
of a particular species. An interesting case of this kind 
occurred in the island of Jamaica ; and what happened in 
this instance by the intervention of man might easily 
occur in connection with changes going on in nature. 
“Twelve years ago rats multiplied enormously in the sugar-cane 
plantations of Jamaica, where they gnawed the sweet stalk, leaving 
the cane which they had attacked, as soon as they had made an 
incision in it, which determined its destruction, and then began upon 
another. This mode of operation entailed a very observable loss 
upon the planters, and they resolved to act energetically. The 
Revue des Sciences Naturelles appliqu e cs tells us how in the meanwhile 
a proprietor in the isle, M. Bancroft Erpent, having brought over 
from India six ichneumons, a species which has constituted itself the 
hereditary foe of rats and serpents ; these animals having rapidly 
multiplied, had soon chased the rodents from the plantations. The 
rats then invaded the farms and villages, the ichneumons pursued 
them thither, and above all destroyed their numerous young in their 
nests. Driven to a new retreat, the rats found another place of 
protection in the summit of various cocoa-nut trees which had just 
been planted in the island ; the ichneumons could not follow them 
thither. After that time the rats lived at peace at the top of the 
cocoa-nut trees, but the planters preferring to hinder them from 
establishing themselves there, set themselves to provide the bottom 
of the trees with a covering of sheet iron, two metres high, nailed 
round the trunk. The suppression of this last refuge made them 
diminish in numbers more and more. As to the ichneumons, so 
useful on their arrival, having no more rats to devour, they have 
turned their attention to the hen-roosts, where they destroy the eggs 
and chickens. They have thoroughly, totally destroyed the quails 
and the partridges of the island, whose eggs, laid on the earth, offer 
an easy prey. They empty them by making a small hole in them, 
and the ignorant mother continues to sit on the sterilised eggs. The 
inhabitants of Jamaica, saved from the rats by the ichneumons, are 
now looking for a new animal which will relieve them of their 
saviours.”—{La Science Pour Tons. Dec. 6th, i8go. p. 392.) 
Another reason of the extinction of species is to be 
found in great complexity of structure. For this com 
plexity of structure not only involves a complex correlation 
of the different organs of the individual body, but also