stupid creatures will starve in the midst of plenty rather than feed themselves. I have had a nest of this species under observation for a long time, but never saw one of the masters feeding, I have kept isolated specimens for weeks by giving them a slave for an hour or two a day to clean and feed them, and under these circumstances they remained in perfect health, while but for the slaves they would have perished in two or three days. I know no other case in Nature of a species having lost the instinct of feeding.
In P. rufescens, the so-called workers, though thus helpless and stupid, are numerous, energetic, and in some respects even brilliant. In another slave-making species, however, Strongylognathus, the workers are much less numerous, and so weak that it is an unsolved problem how they contrive to make slaves.
Lastly, in a fourth species, Anergetes atratulus, the workers are absent, the males and females living in nests with workers belonging to another ant, Tetramorium cœspitum. In these cases the Tetramoriums, having no queen, and consequently no young of their own, tend the young of the Anergetes. It is, therefore, a case analogous to that of Polyergus, but it is one in which slave-owning has almost degenerated into parasitism. It is not, however, a case of true parasitism, because the Tetramoriums take great care of the Anergetes, and, if the nest is disturbed, carry them off to a place of safety.
M. Forel, in his excellent work on ants, has pointed out that very young ants devote themselves at first to the care of the larvæ and pupae, and that they take no share in the defense of the nest or other out-of-door work until they are some days old. This seems natural, because at first their skin is comparatively soft; and it would clearly be undesirable to undertake rough work or run into danger until their armor had had time to harden. There are, however, reasons for thinking that the division of labor is carried still further. I do not allude merely to those cases in which there are completely different kinds of workers, but even to the ordinary workers. In L. flavus, for instance, it seems probable that the duties of the small workers are somewhat different from those of the large ones, though no such division of labor has yet been detected. In F. fusca I made an observation which surprised me very much. In the autumn of 1875 I noticed an ant out feeding alone. The next day the same ant was out by herself, and I could easily recognize her because by some accident she had lost the claws of one of her hind-feet. My attention being roused, I watched the nest for some weeks, and saw this same ant out repeatedly, but no other. This winter I have kept two nests under close observation—that is, I arranged with my daughters and their governess, Miss Wendland, most conscientious observers, that we should look at the nest once every hour throughout the day, and this has been done since the middle of November, with a few exceptions not enough