IK 
VARIABILITY OF SPECIES IN A STATE OF NATURE 43 
specimens: “ The range of variation is so great among the 
Foraminifera as to include not merely those differential char¬ 
acters which have been usually accounted specific, but also 
those upon which the greater part of the genera of this group 
have been founded, and even in some instances those of its 
orders." 1 
Coming now to a higher group — the Sea-Anemones — Mr. F. 
II. Gosse and other writers on these creatures often refer to 
variations in size, in the thickness and length of the tentacles, 
the form of the disc and of the mouth, and the character of 
surface of the column, while the colour varies enormously in 
a great number of the species. Similar variations occur in all 
the various groups of marine invertebrata, and in the great 
sub-kingdom of the mollusea they are especially numerous. 
Thus, Dr. S. P. Woodward states that many present a most 
perplexing amount of variation, resulting (as he supposes) 
from supply of food, variety of depth and of saltness of the 
water ; but we know that many variations are quite inde¬ 
pendent of such causes, and we will now consider a few cases 
among the land-mollusca in which they have been more care¬ 
fully studied. 
In the small forest region of Oahu, one of the Sandwich 
Islands, there have been found about 175 species of land-shells 
represented by 700 or 800 varieties; and we are told by the 
Rev. J. T. Gulick, who studied them carefully, that “ we 
frequently find a genus represented in several successive 
valleys by allied species, sometimes feeding on the same, some¬ 
times on different plants. In every such case the valleys 
that are nearest to each other furnish the most nearly allied 
forms ; and a full set of the varieties of each species presents 
a minute gradation of forms between the mure divergent types 
found in the more widely separated localities .” 
In most land-shells there is a considerable amount of varia¬ 
tion in colour, markings, size, form, and texture or striation 
of the surface, even in specimens collected in the same 
locality. Thus, a French author has enumerated no less than 
198 varieties of the common wood-snail (Helix nemoralis), 
while of the equally common garden-snail (Helix hortensis) 
ninety varieties have been described. Fresh water shells are also 
1 Foraminifera, preface, p. x. 
