16 Observations on the Pulsating Organs [January, 
rent and, at the same time, force along the returning current. 
The outgoing current would almost instantaneously receive an 
impetus from the downward stroke of the anterior end. 
The influence of the pulsating organ on circulation is shown, 
not alone by the energetic movements of the blood currents in — 
its vicinity, but also when the motion ceases in it the blood cur- 
rents stop. I have never observed circulation in the legs while — 
these organs were quiet ; nor have I failed to detect it when they 
were in motion, except in a few specimens too opaque to show 
the blood corpuscles. The stopping and commencing of the 
blood currents, induced by the pulsating organ, have been re- 
peatedly observed. As soon as the pulsatile organ stops, the 
blood currents immediately cease in that particular leg, and the 
first motion of the blood is a slow retrograde movement which 
is particularly noticeable around the pulsatile organ, since here — 
the corpuscles are thickest. A slow oscillation sometimes takes 
place, similar to the movements in a frog’s capillaries, when cir- 
culation is suspended in the web. With the first stroke of the 
pulsatile organ, circulation is resumed, and continues until the 
pulsatile organ again stops. Z 
The influence of each pulsatile organ is confined, as near as I 
can make out, to a single leg, as circulation was noticed in pros 
gress in the body and in other legs during its cessation in one 
leg. 
tively short and independent of each other. Their periods of 
rest sometimes correspond, however, and the pulsatile organs of 
one side of the body may all be in a quiescent state at the same 
time. | : 
My observations on the rate of beating of these organs are 
fragmentary, but, as far as they extend, they show that while con- 
siderable irregularity exists in this regard, the rate of the pulsatile 
organ is always faster than the rate of the heart in the same insect. 
For instance, in Belostoma where the heart beats were from thir- | 
ty-four to forty-five per minute, the pulsating organs were beating 
from 127 to 150 times per minute. In Notonecta, where the 
In their intermittent action the periods of rest are compara- — 
heart was regular at seventy per minute, the pulsatile organs were 
beating 170 to 216 times per minute. In Ranatra the pulsations - 
were several times counted as high as 175 per minute. These 
insects were too opaque to admit of counting the heart bearts. 
a T T E S E ESE CE R 
