292 The Mechanism of Evolution in Leptinotarsa 



product of the external conditions, or at least not entirely so, but in nature I 

 have not been able to find them flying for more than a few yards at any one time. 

 Thus far I have never seen one of these beetles fly more than 75 yards at any 

 one time in nature, and after such a flight I have never seen it repeated, or 

 rarely do they fly again until after some time has elapsed, and on resuming 

 flight they are as apt to return to the original place as to start out in a forward 

 direction, so that the end-result of the flying would, as far as I have seen it, be 

 relatively little or no dissemination at all. From witnessing single exceptional 

 flight and assuming that all flights were in a forward direction, quite false 

 conclusions would be reached. I have followed a single animal for hours 

 at a time in the proper season, with net result of the day's movements — 

 10 or 12 yards' movement from the original starting-point and still within 

 the original colony. On one occasion I followed one female three days 

 at the Chapultepec location. The first day was passed in aimless walk- 

 ing of undetermined length, 87 meters of flight, and 5 hours of rest on the 

 underside of leaves, passing the night in the ground in a crack beside a stone. 

 This was at the height of the flying season in 1905. I returned to the location 

 in the early morning and found the beetle in the same location, and as the 

 morning was cool it did not move from the location until 10 : 23 o'clock, spent 

 the time until noon walking and feeding on the nearby plants, took one short 

 flight of less than 10 meters, and then came to rest on the top of a plant in almost 

 the identical spot from which it had started the day before, moved about on the 

 plant for a few moments, and then crawled down the plant to its foot and under 

 some leaves at the base, from which it did not emerge. I left the location at 5 

 o'clock in the evening, returning the next morning at sunrise, and found the 

 animal in the position in which it was left the night before. About mid-day it 

 crawled up on the plant, remaining about an hour, but the dry, desiccating winds 

 of the early afternoon soon drove it down again into the loose leaves at the foot 

 of the plant, where at 2 o'clock in the afternoon it began burrowing its way into 

 the soil, and in a half hour had passed out of sight. 



This I have every reason to believe is a typical behavior of these animals in 

 these locations; at least nothing to the contrary has been seen to indicate dif- 

 ferently. It seems probable that in these restricted locations there are relatively 

 few instances of interchange in the population, and especially so in those chosen 

 for the examinations made. 



In the course of this study a considerable number of locations of a highly 

 restricted character was investigated, and while most of these were too small to 

 provide the numbers that it was felt should be examined for the work, they did 

 indicate a remarkable degree of difference as a result of the isolation which the 

 topography and the climatic conditions enforced. For example, several loca- 

 tions in the region of the huge larva-flow in the neighborhood of Tlalpam 

 showed exactly this condition in the character of the population, and some of 

 these I saw at least yearly for 6 or more years. 



This condition, prevailing in the valley of Mexico, received further confirma- 

 tion from the data derived in the examination of the populations at the Puebla 

 station and at the location near Chalcicomula, which were so isolated and sepa- 

 rated from the three locations already examined that any interchange of popula- 

 tion is highly improbable, or at least is not of common enough occurrence to be 

 of any moment in analyses as crude as we are, at present, able to make in nature 



