880 THE AMERICAN NATURALIST. [VoL. XXXV. 
case the difference in size is not so striking on account of 
the enormous heads of the latter. The size relations are 
shown in the figures, which represent the soldier, normal and 
macroérgatic workers, drawn with the camera lucida under the 
same magnification. 
Examination even with a good pocket lens reveals the cause 
of the great abdominal development of the macroérgates. One 
sees distinctly the white coils of a parasitic worm distending 
the abdomen till its dorsal and ventral sclerites are widely 
separated by the tense intersegmental membranes. Thus the 
abdomen of the Pheidole comes to resemble externally that of 
replete individuals of the honey ant (Myrmecocystus melliger) 
or our common northern Prenolepis imparis. In some of the 
alcoholic specimens the tense abdominal wall has burst and 
allowed a few of the coils of the parasite to protrude. Such 
specimens may perhaps suggest the way in which the parasite 
ultimately effects its escape from the ant, if indeed it ever 
leaves its host. 
My friend, Dr. T. H. Montgomery, who has kindly exam- 
ined a few of the Pheidoles, writes me that the parasite is a 
species of Mermis. Its exact location in the ant's body is 
not easy to determine, Ze, whether it occupies the lumen 
of the enormously distended crop, or ingluvies, or lies in 
the body cavity outside of the alimentary tract. From 
careful dissection of a single large macroérgate — the one 
represented in the figure — I conclude that the Mermis lies 
within the ingluvies. In this case the head of the parasite 
extended forward through the postpetiolar and into the 
petiolar segment, thus occupying the attenuated neck of 
the ingluvies. The fat-body in the parasitized ants is almost 
or completely absent and the walls of the enormously dis- 
tended crop are practically in contact with the walls of the 
abdomen. The large macroérgate figured contained only 4 
single closely convoluted Mermis, which was ful 50, Me 
long, or ten times the length of the ant. One individual 
dissected by Dr. Montgomery contained two somewhat smaller 
parasites, together with many of their eggs. According to 
Dr. Montgomery, the parasites are “either fully mature Or 
