1927] 
The Slave Raids of Harpagoxenus americanus 
25 
return of the raiders is rendered impossible then a fragmentary 
mixed Harpagoxenus-Leptothorax colony results. 
The phylogeny of Harpagoxenus has been a matter of con- 
siderable speculation. The development of its raiding habits, a 
point formerly much disputed, is now agreed as paralleling that 
of Polyergus. . Viehmeyer (‘21) eventually concluded that his 
hypothesis of the lestobiotic derivation of the raids of this ant 
was untenable and accepted the above explanation. On the 
other hand, there has never been any doubt of the close morpho- 
logical affinities of Harpagoxenus to Leptothorax. L. acervorum 
(subgenus Mychothorax) is considered as closely related to, or 
identical with the ancestral form. It is generally believed that 
the parasitic ants (intraspecific parasitoids) have been devired 
from those species which they parasitize. (Wheeler T9). Oc- 
casionally when the parasitic relation has been of long standing 
the original host may have become rare or extinct and have been 
replaced by another closely related to it. The relation of Har- 
pagoxenus to its slaves clearly illustrates both these points. 
The resemblance between the European H. sublcevis and L. 
acervorum, its usual host, is close. On the other hand II . amer- 
icanus parasitizes either L. longispinosus or curvispinosus, neither 
of which it particularly resembles. This is exactly what we 
should expect from the distribution of the host species. L. 
acervorum, a dominant ant in the European palseartic fauna, is 
rare in North America. The dominant neartic forms in this 
country are L. longispinosus and L. curvispinosus. It would be 
expected that the American Harpagoxenus would have adopted 
these forms in place of the rare acervorum. 
In the study of phylogenetic relationships the males play 
an important part because of their morphological stability. 
Since the males of H. americanus have been hitherto unknown it 
seems advisable to devote a brief survey to the phylogeny of this 
ant. Through the kindness of Dr. Wheeler I have been enabled 
to examine material in his collection, and on this the following 
comparisons were made. We should expect morphological sim- 
ilarities to be most manifest in the males of the two genera and 
least apparent in the workers. Nevertheless even the latter 
exhibit a number of significant features in common. The work- 
