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 Lcplolhorax 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 excc])tions; 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 m 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. lotigispinosus 

 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 Formicida?, as shown 

 in the following conspectus: 



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

 with Formica rttja. 



" 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 Cremastogasier lincolata, the common shed- 

 builder ant of the north and east.] 



"3. L. pcrgandei lives, probably as a guest, in the nests of Monomorium 

 miniUum, var. minimum. 



"4. The single colony of the Mexican L. pcliolatus which I h ive seen 

 was living in parabiosis [interlacing nest] with species of Cryptocerus and 

 Cremastogastcr. 



"5. L. tuheriim, var. iinijasciatus, lives with the European Fonnicoxenus 

 ravouxi, the relations between the species being, perhaps, the same as those 

 which obtain betw-een Formica ruja and Formicoxenus nilidulus. 



"6. L. muscorum, L. acercorum, and L. tubcrum live as slaves or auxili- 

 aries with the European Tomognathus sublwi'is. 



"7. L. curvispinosus probably performs the same role in the nests of 

 T. Americanus. 



"8. L. tuberum has been found associated with Slrongylognathus testa- 

 ceus. Here, too, the Leptothorax probably acts as the slave of the dulotic 

 species. 



"9. L. emersoni lives with Myrmica brex'inodis as described [on p. 544]" 



