THE NAUTILUS. 
77 
been found elsewhere near the locality. The large quantities found 
would point to their having been native to the place for a long 
period of time. Why they had not spread is not strange when their 
habits are considered: they are slow in movement and retiring,, 
loving to adhere to the under side of a stone, where moisture can. 
be procured in the hot days of summer. Surrounded by conditions 
favorable to their existence, they neither seek nor require change 
of locality. 
It is easy to account for the introduction in any place of a new 
plant or insect. The influence of the wind will scatter spores or 
seed vessels over a vast area ; whilst when the locomotive powers of 
insects are considered, both aerial and terrestrial, it needs but a 
new condition, generally the scarcity of food, to cause an immediate 
migration, bounded only by arrival at the nearest spot indicated by 
instinct as the place where more suitable conditions exist, necessary 
to the preserval of life and development. But in the case of a 
snail, and especially such a slow moving one as S. hirsuta, it is 
different; to such an organism transition over an extended distance 
would be an impossibility, that is to say, by its own natural 
powers. 
The only theory possible to solve this question is that they were 
carried there either as snails or the spawn of snails by some out¬ 
side influence which we can only attribute to a winged animal 
capable of covering an extended distance continuously ; for exam¬ 
ple, a hawk or other bird of strong flight may have left the Pali¬ 
sades of the Hudson river with dirt adhering to its claws containing 
the embryo “hirsuta,” and winging its way across river and land, 
alighted on a tree at this spot, and in the process of perching, 
scraped oft’ dirt and snail spawn, which dropped amongst the stones 
below. And again, the bird may have swallowed the S. hirsuta , 
and as it is a globular shell and of very hard substance, it may have 
escaped the grinding of the stones in the oesophagus, passed through 
the digestive organs, and been ejected at the locality with other 
excrement, and there perpetuated the species. 
At any rate, this appears the only agency by which the species 
can have been introduced, and unless the same can be distinctly 
refuted, it forms a theory illustrated by the present example of the 
diffusion of certain forms of molluscan life over a continent — an 
agency probably uncommon and rarely put in force by the strange 
workings of Mother Nature. 
