722 THE AMERICAN NATURALIST. [VoL. XXXV. 
considerable light on the extent to which such unions are 
possible. Forel (74) and Wasmann (91) have recorded a num- 
ber of interesting observations, some of which are very similar 
to the following cases observed in America. 
26. Formica pergandei Emery and F. pallide-fulva Latr. 
Mr. Pergande (Emery, '933, p. 646) found near Washington, 
D.C., a mixed colony of Formica pergandei and the typical 
F. pallide-fulva, but the nature of the consociation was not 
determined. Emery suggests that the former species may be 
a true dulotic ant and F. pallide-fulva its auxiliary species. 
Mr. Pergande informed him that he had known of the exist- 
ence of this colony for several years, but had seen only pallide- 
Julva in the nest till the summer of 1892, when the 7. pergandet 
made their appearance in the colony. This observation would 
seem to favor an explanation by alliance rather than dulosis, or, 
at any rate, on the suppositon of dulosis the róles of the two 
species would seem to be the reverse of that suggested by 
Emery, pallidefulva being the dominant and fergandei the 
auxiliary species. 
27. Formica exsectoides Forel and F. subsericea Say. 
Forel (00°, p. 12) found a small mixed formicary of these 
species at Hartford, Conn. “There could be no doubt con- 
cerning the intimate life in common of the two species in the 
same nest. They entered and went out through the same 
doors, etc." Rev. P. J. Schmitt writes me that he has found 
at different times five different nests of F. exsectoides-sub- 
sericea, These invariably contained females of the exsectoides 
only. All these colonies were, moreover, obviously incipient, 
as shown by the fact that they contained scarcely more than 
fifty ants, including both species. These six cases observed 
by Forel and Schmitt are probably of the same nature as the 
very similar cases of F. ersecta-fusca, F. truncicola-fustt, F. 
exsecta-pressilabris-fusca, F. pratensis-fusca, and F. — 
t 1$ 
rufa-fusca described by Forel (74) and Wasmann (91). 
probable that the American ersectoides, like the Europea" 
