1918] Richardson—Pulsatile Vessels in Legs of Aphidide 15 
to another, that an entirely different condition may, of course, 
present itself in 1918. We mean that the worms may not be so 
plentiful for some reason and if this should prove true, it will be 
difficult to obtain very much information. 
From our observations this summer (1917) we firmly believe 
that the nematodes accomplished an immense reduction in the 
number of grasshoppers near Dummerston Station, Vermont. 
This worm, if its life-history is investigated, might offer possibilities 
for introduction into regions where it does not occur and where 
grasshoppers are a pest. For this reason, and because we were 
unable to find any records of such a high degree of parasitism, we 
thought it best to present these preliminary observations. 
THE PULSATILE VESSELS IN THE LEGS OF APHIDIDA. 
By Cuas. H. Ricuarpson, 
College of Physicians and Surgeons, Columbia University, New 
York City. 
When one of the light-colored aphids, like Myzus persice Sulz., 
is mounted alive on a depression slide, a rapid beating motion can 
be detected with the low power of the microscope in the tibia of 
each leg just below its juncture with the femur. These centers of 
activity mark the position of the pulsatile vessels. 
The structure of these minute and delicate organs in aphids is 
difficult to determine, but serial sections through the tibia show 
that they are undoubtedly tubular. In the large aquatic Hemip- 
tera, where they were first studied, the structure is more easily 
seen. Berlese! describes them as tubular organs crossed obliquely 
with numerous muscle bands and continuous with a non-pulsating 
part on either side. 
The function of these organs 1s clearly one of blood propulsion. 
Locy,? who studied them in the aquatic Hemiptera, was able to 
discern the direction of the blood currents in the immediate vicinity 
of the pulsatile vessels, one current moving inward, the other out- 
ward. In Myzus persice, upon which most of my observations 
1 Gli Insetti, Milano, 1909, p. 764, fig. 953. 
2 American Naturalist, Vol. 18, pp. 13-19, 1884 (1 pl.). 
