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 

 ana 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 Formicidae, as shown 

 in the following conspectus: 



"i. The European L. muscorum often lives in plesiobiosis [double nest] 

 with Formica rufa. 



" 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 hive 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]." 



