Page:Popular Science Monthly Volume 59.djvu/296

286 Now, when the Helices of California, Mexico and a part of those of the West Indies were examined, it was found that they have the dart apparatus, agreeing with species of Japan, China and the Philippines, not with those of Europe or of eastern North America; for, to emphasize this resemblance, the Helices of the middle and eastern United States are anatomically totally unlike the Californian, Mexican and Antillean, having no dart-sack or mucous gland.

We are, therefore, confronted with a group of snails inhabiting both borders of the greatest ocean, but agreeing so closely in anatomy that no hypothesis but that of a common origin, descent from common ancestors, is conceivable. Our American dart-bearing Helices must surely look to distant shores in far-off times for their ancestry.

Map showing distribution of Dart-bearing Helices in Vertical Lines. Cretaceous Sea in Broken Horizontal Lines. Being on Mercator's Projection, the Northern Ranges of the Dart-bearers in America and Asia appear much more separated than they really are.

We know, however, that in Upper Cretaceous times the Arctic lands were not, as now, clad in the scanty green of mosses, lichens and herbs, with few deciduous trees, except stunted willows and the like, but they bore noble forests of magnolia, beech and birch, with red-woods and pines—such forests as snails love and thrive in, doubtless