1918] Richardson — Pulsatile Vessels in Legs of Aphididw 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 APHIDIDiE. 



By Chas. H. Richardson, 

 College of Physicians and Surgeons, Columbia University, New 



York City. 



Wlien one of the light-colored aphids, like Myzus persicoe 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 is 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 persicoe, 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 pi.). 



