Ill 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." ^ 



Coming now to a higher group — the Sea- Anemones — Mr. P. 

 H. Gosse and other "HTiters 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 mollusca they are especially numerous. 

 Thus, Dr. S. P. Woodward states that many present a most 

 perplexing amount of variation, resulting (as he supj^oses) 

 from supply of food, variety of depth and of saltness of the 

 water ; but Ave 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 

 Kev. 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 fmins between the more 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 

 ^ Foraminifera, preface, p. x. 



