investigation among the ruins of Yucatan and Campeche not as many specimens of worked obsidian were found as could be picked up in half an hour among certain Mexican ruins; but traces of ancient fabrication of flint implements were more plentiful than anywhere else. =The Seventeen-Year and the Thirteen-Year Locusts.=--The periodical cicada, or seventeen-year locust, as it is called, is distinctly American, and has the longest life period of any known insect. It is especially remarkable, Mr. C. L. Marlatt observes in his memoir upon it, in its adolescent period, the features of particular divergence from other insects being its long subterranean life of thirteen or seventeen years, and the perfect regularity with which at the end of these periods every generation, though numbering millions of individuals, attains maturity almost at the same moment. At this moment the brood issue from the ground, leaving innumerable exit holes, and swarm over trees and shrubs, filling the air with their strident calls, and laying their eggs in slits which they cut in the trees. The larvæ, when hatched, fall to the ground, and quickly burrow out of sight, each "forming for itself a little subterranean chamber over some rootlet, where it remains through winter and summer, buried from sun, light, and air, and protected in a manner from cold and frost.... It lives thus alone in its moist earthen chamber," rarely changing its position unless some accident to the nourishing rootlet may necessitate its seeking another, passing the thirteen or seventeen years of its hypogeal existence in slow growth and preparation for a few weeks only of winged life in the air and light. Other cicadas appear every year, usually in comparatively small numbers. They are probably equally long in maturing, but the periods of their lives have from some cause or another been cast in "off" years. The thirteen-year broods are southern, and the shortening of their periods of development may possibly be accounted for by the longer season of warmth in the southern year giving them the number of hours or of aggregate degrees of warmth in thirteen years that the more northern broods can not receive in less than seventeen years. This, however, is only speculation, and there are difficulties in applying the supposition to make it fit all the facts; and many believe that the two races are specifically different. The late Prof. Charles V. Riley distinguished twenty-two different broods of cicadas in the United States, seven of which appertain to the thirteen-year period (_Cicada tredecem_). MINOR PARAGRAPHS.