558 
Saw-flies, Gall-flies, Ichneumons, 
rocal advantages, once begun, could readily be developed into such a curi¬ 
ous condition as that, for example, of Myrmica and Leptothorax described 
on p. 544. The beginning of such an association requires the assumption, 
of course, that the apparent general rule of mutual animosity existing among 
ants shall have its natural exceptions; that their instincts are not wholly 
immutable or all embracing. To take a particular case, Wheeler has admi¬ 
rably shown the remarkable differences of instinct exhibited by the species 
of the single genus Leptothorax. While systematists agree that this large 
and widely distributed genus is unusually homogeneous, Wheeler shows 
that in habits its species are singularly diverse: “Many of the forms have 
no tendency to consort with ants of other species, but differ considerably 
in the stations which they inhabit. Some prefer to live under stones, others 
in moss, others under bark or in dead wood, and still others, like one of the 
Texan species, in cynipid galls, or, like our New England L. longispinosus 
Rog., in the worm-eaten hickory-nuts among the dead leaves under the 
trees. Many species, however, have a pronounced penchant for entering 
into more or less intimate symbiotic relations with other Formicidse, as shown 
in the following conspectus: 
“1. The European L. muscornm often lives in plesiobiosis [double nest] 
with Formica ruja. 
“2. A similar tendency is undoubtedly exhibited by our American L. cana¬ 
densis Provancher, which I have had occasion to observe since the second 
part of this paper was written.” [Here Wheeler describes in detail the 
symbiosis of L. canadensis and Cremastogaster lineolata , the common shed- 
builder ant of the north and east.] 
“3. L. pergandei lives, probably as a guest, in the nests of Monomorium 
minutum, var. minimum. 
“4. The single colony of the Mexican L. petiolatus which I h ve seen 
was living in parabiosis [interlacing nest] with species of Cryptocerus and 
Cremastogaster. 
“5. L. tuberum, var. unijasciatus , lives with the European Formicoxenus 
ravouxi, the relations between the species being, perhaps, the same as those 
which obtain between Formica ruja and Formicoxenus nitidulus. 
“6. L. muscorum, L. acervorum , and L. tuberum live as slaves or auxili¬ 
aries with the European Tomognathus sublcevis. 
“7. L. curvispinosus probably performs the same role in the nests of 
T. Americanus. 
“8. L. tuberum has been found associated with Strongylognathus testa- 
ceus. Here, too, the Leptothorax probably acts as the slave of the dulotic 
species. 
“9. L. emersoni lives with Myrmica brevinodis as described [on p. 544]-” 
