15^ ANTS. 



Middle Stairs a similar relation obtains between the glade and iield 

 faunas, which it is often impossible to separate by a hard and fast line. 

 l : ormica sclianfiissi. for example, seems to occur indifferently in 

 either station. 



With the exception of the sand and desert associations, which de- 

 pend very largeh mi physical conditions, like soil, warmth and mois- 

 ture, the above list comprises mainly adaptations to particular types 

 of vegetation. Other associations of a similar character undoubtedly 

 exist in other countries, especially in the tropics, where the relations 

 between ants and plants are often more intimate than in temperate 

 regions- A very striking ethological association, depending on rela- 

 tions to the soil and consisting of species common to many of the above 

 groups, is represented by the so-called hypogaeic ants. These occur 

 in all parts of the world, and, owing to their exclusively subterranean 

 life, have acquired a peculiar adaptive facies. They are aptly de- 

 scribed by Emery (18750) as "the inhabitants of the most remote and 

 obscure hiding places of the soil, dwellers in the narrow crannies 

 beneath the heaviest rocks, in the very pores of the earth, blind and 

 amblyopic pygmies of slow gait and strangely varied forms, micro- 

 scopic remnants, so to speak, of extinct genera, that have found in the 

 bosom of the earth a respite from the invasion of more robust and 

 prolific types." As a rule these hypogreic ants are of small size, pale 

 color and have no eyes or only vestiges of these sense-organs, although 

 all of these peculiarities may be found in certain epigaeic species. We 

 find, indeed, all gradations in habits between ants that live in exposed 

 situations and extremely hypogaeic forms, and there can be no doubt 

 that the latter ethological group has been recruited from unrelated 

 genera among the former. As nearly all ants live much of the time 

 in dark subterranean galleries and chambers, the transition to a com- 

 pletely hypogaeic habit is easily effected, especially when food is more 

 accessible in the soil than on the surface, or when larger and more 

 pugnacious ants make life at the surface intolerable. But no matter 

 how hypogaeic a species may become, it always retains enough of its 

 ancestral habits to come to the surface for the nuptial flight of the 

 males and females. At such times the blind and etiolated workers 

 excavate a gallery to the surface and conduct the winged sexes to the 

 opening. Tn \ T orth America there are hypogaeic species of Eciton. 

 Sti^inatoinina, Ceraf>achys, Sysphincta, Proccratiuni, Pmicra, Solc- 

 nopsis, I : .rcb oin \nna, Stntini^cnys and Lasins, and in other parts of 

 the world species of the genera Dory/us, Lcptauilla, Aeromyrma, />/>- 

 louwrhtm, Epitritns, Rlwpalothri.r, etc., have very similar habits, 

 although these in most cases are very imperfectly known. Facts of 



