Some fifteen years ago I mentioned in an article, entitled “Insect Pets,” a pair of flies, the common _Musca domestica_ of our houses, which had been closely observed by Mr. Forestel, the gentleman who at that time had charge of the distributing department of the Philadelphia _Record_. This position necessitates nocturnal employment. While taking his midnight lunch, Mr. Forestel’s attention was directed to a pair of these insects that had located themselves upon his plate. Had it been in the summer when flies were plentiful, the event would hardly have been noticed; but being in the winter, a season notable for their great scarcity, they could not but impress his mind with something out of the ordinary. Night after night these self-invited and curious guests presented themselves at the same place, and it was a long time before he observed the regularity of their visits. At first he was disposed to view the alighting of two flies upon his plate as a mere coincidence, but he at length became so deeply interested in the affair, that he resolved to watch their actions very closely. It was not long before he became convinced that they always waited for the commencement of the meal, when they would deliberately fly down for their regular lunch. So closely did he watch them, that he was soon able to discriminate between the two, and to discover beyond a doubt that it was not a series of two flies, but always the same pair. As time progressed, Mr. Forestel and the flies grew to be famous friends. They in time became so friendly, that they would permit themselves to be handled. Although at first they would only appear when Mr. Forestel was alone, yet they soon became accustomed to strangers. On the nights when their friend was not on duty, others have spread their lunches on the table used by him, but the flies were not slow in making the discovery, and, instead of alighting, would quickly hasten away without their accustomed meal. Who can deny the possession of memory to these two flies? Had the discovery of the food been an accidental occurrence the first time, could it have been so the second and all the succeeding times? Then, again, the flies always came at the right time, showing that they had some idea of the passing moments. Even admitting that this latter thought is out of the range of probability, there can be no doubt that they were not observant creatures, else how would they know when to come, or whether or not the man that sat at the table was the same that had shown them so much kindness on their previous visits. That they did know these things, there cannot be the slightest doubt. But how did they know them? There is only one answer to the query. They knew them through the exercise of memory, these creatures impressing on their minds the appearance of the objects near the table, the form and color of the table itself, the look, manner and dress of the man who sat by it, and acting on the result of these impressions. Human beings act in