792 THE AMERICAN NATURALIST. [Vor. XXXV. 
symbiosis. Both the stress laid on the psychical manifesta- 
tions of ants and the attempts at establishing a phylogeny 
of the compound and mixed nests have been clearly appre- 
hended and set forth in considerable detail by Wasmann (91). 
While my own observations lead me to agree with this able 
investigator in many respects, I must, nevertheless, dissent 
from his attitude towards the genetic method as applied to 
the study of the compound and mixed nests. It is necessary, 
therefore, to attempt a critical revision of this matter so far 
as this is possible within the limits of the present paper. I 
shall deal first with phylogeny as applied to the cases of social 
symbiosis and conclude with a very brief consideration of some 
of the pertinent psychical problems. 
Darwin was the first to attempt an explanation of the origin 
of dulosis in the European ants. In a well-known passage in 
the “ Origin " ('61, p. 244) he says: “ By what steps the instinct 
of Formica sanguinea originated I will not pretend to conjec- 
ture. But as ants, which are not slave-makers, will, as I have 
seen, carry off pupz of other species, if scattered near their 
nests, it is possible that such pupz originally stored as food 
might become developed; and the foreign ants thus uninten- 
tionally reared would then follow their proper instincts, and do 
what work they could. If their presence proved useful to the 
species which had seized them — if it were more advantageous 
to this species to capture workers than to procreate them — 
the habit of collecting pupz originally for food might by nat- 
ural selection be strengthened and rendered permanent for the 
very different purpose of raising slaves. When the instinct 
was once acquired, if carried out to a much less extent even 
than in our British F. sanguinea, which, as we have seen, is 
less aided by its slaves than the same species in Switzerland, 
natural selection might increase and modify the instinct — 
always supposing each modification to be of use to the species 
— until an ant was formed as abjectly dependent on its slaves 
as is the Formica rufescens.” 
Apart from the statement that the English and Swiss sa” 
guinea differ in their behavior —a statement ‘which has been 
since disproved — Darwin’s views have been accepted by Forel 
