22 William Morton Wheeler. 



These specimens also show that the mites had already acquired the 

 peculiar habit of affixing 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 singular 

 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. fiori 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 for this pur- 

 pose. As it has recently been shown by Emery, Wasmann and 

 Crawley that Lasius umbratus and L. fuliginosus 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 aud 

 specialization in minor instincts, but the differentiation of the sub- 

 families and genera of many species, of polymorphism, of the larval 



