Wasps, Bees, and Ants 
559 
It is evident, therefore, says Wheeler, that the ants of this genus 
have originally possessed certain traits which made it specially easy for 
them to enter into symbiotic relations with other species of ants. Some 
of these fundamental or original traits may still be recognized in the genus, 
to wit: 
“i. The genus has a very wide geographical distribution, a prerequisite 
to the establishment of such numerous and varied relations with other ants. 
“2. The species are all of small size. This must undoubtedly facilitate 
their association with other ants. 
“3. The colonies consist of a relatively small number of individuals. 
This, too, must greatly facilitate life as guests or parasites in the nests of 
other ants. 
“4. Most of the species are rather timid, or at any rate not belligerent. 
They are, therefore, of a more adaptable temperament than many other 
ants even of the same size (e.g., Tetramorium coespitum). Forel has 
shown that L. tubero-a]finis will rear pupae of L. mylanderi and even of 
Tetramorium ccespitum and live on good terms with the imagines when they 
hatch. 
“5. There is no very sharp differentiation in habits between the queens 
and workers of Leptothorax. This, too, should facilitate symbiosis. The 
queens, as I have shown in the case of L. emersoni , may retain the excavating 
instinct and the instincts which relate to the care of the larvae. 
“6. The similarity in instinct between the queens and workers of Lepto¬ 
thorax finds its physical expression in the frequent occurrence of interme¬ 
diate or ergatogynous forms. So-called microgynic individuals, or winged 
queens no larger than the workers, have been frequently observed by Forel 
and Wasmann in L. acervorum . Those observed by the latter author also 
showed color transitions between the normal queens and workers.” 
Finally, Wheeler points out that this heterogeneity of habit and these 
■existing gradatory steps between strictly non-working fertile queen and 
strictly non-fertile working-worker, are evidence for the selection theory as 
explaining the division of labor and differentiation of structure in the special¬ 
ized ant communities. “Viewed as a whole, these different symbiotic rela¬ 
tions cannot be said to bear the ear-marks of internal developmental causes 
operating in a perfectly determinate manner. Indeed, appearances are 
quite otherwise and seem rather to point to indeterminate variations which 
have been and are still in process of being seized on a fixed by natural selec¬ 
tion. It must also be admitted that the same appearance is presented by 
the whole complex of conditions in compound and mixed nests, but the 
demonstration is more cogent when it can be shown that we have relations 
as different as those of dominant species (L. emersoni ) and slaves (L. acer- 
