as Forel has shown, and as I was able to observe during the past June in a large Anergates-Tetramorium colony at Vaux, Switzerland. This colony contained upwards of 1,000 winged female Anergates and several hundred males. Many of the former, placed on the craters of strange Tetramorium nests, entered these at once. The Tetramorium workers never killed these females, though they often seized them, carried them some distance from the nest and cast them away. The males, too, were not killed, although they were more forcibly and immediately ejected. This behavior is very suggestive, for Tetramorium workers when placed on the craters of strange colonies of their own species are at once pounced upon and killed.
It is not improbable that all three of these derivative types, namely, temporary, permanent and dulotic parasitism, have developed independently out of the primitive adoptive type of colony formation, although the details of this development are still very obscure. I have already given my reasons for believing that slavery did not arise directly from temporary parasitism. Owing to the excessive specialization of the permanent parasites and the loss of the worker caste among these species, it is not so easy to determine whether they have arisen from temporarily parasitic or from dulotic species, for it is conceivable that they may have arisen from either, especially as there are other ants, such as Strongylognathus and Tomognathus, which combine peculiarities of both of these categories. The species of Strongylognathus are peculiar to the palearctic fauna and, like Anergates, live with colonies of the extremely abundant and ubiquitous Tetramorium cæspitum. The workers and females have sickle-shaped mandibles like Polyergus. Two species, S. rehbinderi and S. huberi, as Forel has shown, still possess vestiges of slave-making instincts. In S. testaceus, however, which is the common European form, the workers are greatly reduced in number, showing, as Forel has suggested, that this caste is on the eve of disappearing completely and thus leading to conditions like those of Anergates and the other permanent parasites. Wasmann once found a S. testaceus-Tetramorium colony containing fertile females of both species, and during the past June Professor Forel and I found a similar colony on the Petit Salève, near Geneva. This colony contained a fertile Tetramorium queen. The much smaller Strongylognathus queen could not be found, but must have been present, as there were young pupæ of this species in the nest. It is evident in this case, therefore, that the parasitic and host queens manage to live side by side (allometrobiosis of Forel). This condition arose, perhaps, from slavery or temporary parasitism by a suppression on the part of the Strongylognathus queen of the instinct to kill or drive away the Tetramorium queen.
The genus Tomognathus is represented in northern Europe by T.
