No. 418.] NESTS OF AMERICAN ANTS. 793 
(74, p. 440), who has also called attention to the fact that the 
frequent occurrence of pupae without cocoons in the nests of 
F. fusca would add to the plausibility of Darwin's hypothesis, 
for such free pupze would be able to hatch without the assist- 
ance of the enslaving species.! 
Pursuing Darwin's line of thought, Forel (74, p. 443) 
called attention to the following series, which seems to have 
been previously in great part suggested by von Hagens (67): 
“1, Working ants pure and simple; 2. ants dwelling in 
abnormal mixed colonies; 3. F. sanguinea (sometimes with- 
out slaves); 4. Polyergus rufescens (here the working instinct, 
which is merely diminished in F. sanguinea, disappears com- 
pletely and the slave-making instinct attains its apogee) ; 
5. Strongylognathus huberi (the slave-making instinct is cer- 
tainly still alive); 6. S. ¢estaceus (the slave-making instinct 
no longer exists except in the form of derisory vestiges, the 
worker is on the road to atrophy and tends to disappear) ; 
7. Anergates atratulus (the worker has disappeared ; only para- 
sitism is admissible). This last ant, it seems to me, is a 
remarkable example of reversion to ancestral traits (incom- 
plete societies, without workers) through parasitism ; its gene- 
alogy is explicable through S. ¢estaceus, the workers of which 
have become so rare in comparison with the females and 
males." Essentially the same series of cases was adopted by 
Lubbock (94, pp. 88, 89). At the present time it could be 
still further perfected, as Wasmann suggests, by the insertion 
of Tomognathus sublevis between F. sanguinea and Polyergus. 
The views initiated by Darwin have not been allowed to 
pass unchallenged. The first to take up the cudgels was 
McCook in the concluding paragraphs of his paper on Polyer- 
gus lucidus (80, pp. 383, 384). After presenting Darwin's 
views he writes: «Whatever credit we may give to this 
ingenious hypothesis, it must be said that in the case of our 
F. schaufussi, natural selection has not operated to degen- 
erate the soldierly courage and faculty, and remand the duty 
of defense to those associates in whom the military faculty 
1 The American slaves of Z. sanguinea and Polyergus, viz., F. fusca, Vats., sub- 
sericea and subenescens, and F. nitidiventris also often have free pup®. 
