But this curious parasitic relation between ant and fly is not confined to the larval stage of each. Continued observation led to a further discovery which I give in Professor Wheeler’s own words: “As the days passed, the mature ant-larvæ spun their brown cocoons one by one, and one by one the mature commensals (the larval parasites, that is to say) disappeared. No traces of them could be discovered. The only remaining resource was to open the cocoons. Five were opened, and in two of recent formation commensals were found! Having shared the table of their host, they had come to share its bed as well. The dipteron (the parasite, as I have said, is a fly) had pupated after the manner of its kind, forming a puparium, that is, instead of spinning a cocoon like the ant larva: the dead larval skin, somewhat shrivelled and contracted, was used as an envelope, and within this the pupa proper was found. In all cases the puparium was located in the caudal pole (at the bottom) of the ant cocoon, and was immovably stuck to the wall of the cocoon, its anterior end directed towards the cephalic pole”[14] (the top). But what, asks Professor Wheeler, does the commensal larva do “while the ant-larva is weaving its cocoon? Does it move about to avoid the swaying jaws of the spinning larva? or does it take up its position, from the first, at the posterior end of the larval ant, and there remain motionless while the posterior pole of the cocoon is being completed? It is very difficult to answer these questions.”[14] One might think that young ants thus deprived, day by day, of a portion of every meal, would be stunted in their growth, and not make such large and healthy workers as those who had never been encumbered with a parasite. This, however, does not seem to be the case, and no difference can be detected between the one and the other. Perhaps, therefore, ants habitually eat, if not more than is good for them, at least more than they require. This is the case almost universally amongst civilised men, at least in Northern Europe, and with savages to a still greater extent whenever the wherewithal is at hand. In the above case we have, as Professor Wheeler remarks, a very perfect example of what is termed commensalism, in the original meaning of the word—that is to say, of two or more individuals dining together at the same table. As applied to natural history, the individuals in question must be of different species, but it is not often that the definition otherwise is so rigorously adhered to.