EFFECT OF SETTLEMENT UPON INDIGENOUS VEGETATION. 207 
ment) are the most prominent. Of the Mollusca twenty-four” 
species of foreign snails and slugs have been introduced, a list of 
which is given by Mr. C. Musson. + 
There are several introduced earthworms, which certainly have 
an effect in loosening and fertilising soil, but in view of the very 
large number of indigenous species and individuals of these animals 
found in Australia, their work need not be considered. It is 
remarkable however, how widely they have spread, introduced 
earthworms have been collected far beyond Bourke. 
(a) Direct destruction of flora by introduced animals. 
Taking rabbits and hares first, there can be no question but 
that they destroy immense quantities of plants. In an ordinary 
season when grass is fairly plentiful, their ravages are chiefly con- 
fined to that, and they do little harm in that way. But when a 
dry season comes, and food is scarce, hunger drives them to courses 
they do not ordinarily take. Their habits change under the 
pressure of starvation, which bears out what has been said by 
Chas. Darwin of the innate plasticity of constitution in organisms 
becoming active when they are removed to new habitats and 
surroundings. They have been accused (I am not prepared to say 
with how much truth) of swimming rivers and climbing over wire- 
net fences in their migrations in search of food. It is certain 
that in the western plains, the scrub over large areas has been 
killed by their gnawing the bark off (a habit which has been taken 
advantage of in killing them, poisoned twigs being scattered about 
their haunts) and it is well known that they climb bushes to get 
at leaves, young twigs and bark, an addition to their powers since 
they reached Australia, as a climbing rabbit was never heard of 
in England. In numerous localities, areas of many square miles 
have been denuded of all grasses and herbaceous plants, the roots 
dug up and devoured, and the bushes killed as above mentioned. 
In the report before quoted, Mr. Torrens says, “ In the driest spots 
* Since writing the above, Mr. Hedley has been good enough to look 
carefully into this question and he raises the number to twenty-six. 
+ Proc. Linn. Soc. of N.S. Wales, 2nd Series, Vol. v., p. 883. 
