22 
.William Morton Wheeler. 
These specimens also show that the mites had already acquired the 
peculiar habit of af fixing themselves to very definite regions of their 
host’s integument. 
Not only had the ants of the Lower Oligocene acquired very 
interesting relations with other insects, but they had, in all probability, 
established parasitic relations with one another like those found among 
the recent slave holders and temporary social parasites. I have examined 
the clypeus of all the specimens of Formica in the hope of finding 
the fore-runner of F. sanguinea, though in vain. But the singulär 
ant, which I have called Pityomyrmex tornquisti, notwithstanding the 
fact that it belongs to the subfamily Dolichoderince, bears a striking 
resemblance to the living palearctic Polyergus rufescens and may have 
had similar habits. Formica phaethusa, which is very closely related 
to F. truncicola, is a member of the rufa group, and since all the 
known forms of this group are temporary social parasites, as Wasmann 
and I have shown, it is very probable that the amber species established 
its colonies with the aid of F. flori colonies, just as the modern F. 
truncicola and rufa and their various subspecies (integra, obscuriventris, 
pratensis, etc.,) use F. fusca or some one of its varieties f or this pur- 
pose. As it has recently been shown by Emery, Wasmann and 
Crawley that Lasius umbratus and L. fuligmosus are tempory social 
parasites, the former on L. niger, the latter on L. umbratus , we may 
infer that the amber L. nemorivagus, which is very closely related to 
L. umbratus, was probably a temporary social parasite of L. schieffer- 
deckeri. And as the living forms most closely allied to Erebomyrma 
antiqua ( Carebara vidua, Aeromyrma nossindambo and Erebomyrma 
longi) live in lestobiosis with termites, we may assume that the amber 
species had very similar habits, especially as several species of termites 
are known to occur in the same geological formation. 
The general impression thus left on the mind by a study of the For- 
micidce is one of wonder at the great exuberance of the group in 
the early Tertiary of Europe and the conviction that since this period 
the family has not only failed to exhibit any considerable taxonomic 
or ethological progress but has instead suffered a great decline in the 
number of species and therefore also in the variety of its instincts, 
at least in Europe. There has, undoubtedly, been a development of 
many new species, subspecies and varieties and an elimination of many 
stenothermal forms in various parts of the world during the late 
Tertiary and the Quaternary and possibly also a greater precision and 
specialization in minor instincts, but the differentiation of the sub- 
families and genera of many species, of polymorphism, of the larval 
