TE Observations on the Pulsating Organs [January, 
integument of the legs was scraped very thin. The organs can 
be demonstrated in this manner, even in the thick legs of the 
adult Belostomæ. — 
The organs are most easily seen in the legs of Notonecta and ~ 
Corixa, but are not so large and pronounced as in the legs of the $ 
Nepide. In the more transparent individuals not only are the 
organs readily seen, but the circulation of the blood can be 
watched with a power high enough to bring out the corpuscles. 
The pulsating organs were noted in the following genera: 
Corixa, Notonecta, Gerris, Belostoma, Perthostoma and Ranatra ; . 
particular attention having been given to the organs in Belos- _ 
toma, Perthostoma and Ranatra. 
Description.—These organs are found in the three pairs of legs 
of all the genera mentioned above. They are generally in the 
tibia of the leg, just below its articulation with the femur. In the 
raptorial legs of Ranatra, however, the organs are in the clasp- 
joint or tarsus just below its articulation with the tibia. 
Examined with a power of seventy-five diameters, they appear 
as little whip-like organs pulsating rapidly. In the Nepidz they 
lie outside the median line of the leg, towards the front side, be- _ 
ing slightly convex: towards the outside. This curved body | 
which forms the bulk of the pulsatile organ, is attached at both 
ends and from its sides several attachments extend upwards and 
backwards to the integument of the leg (see Fig. 4). 
The shape in Corixa and Notonecta is quite different ; it is 
somewhat hand-shaped in Notonecta, and in Corixa the shape of 
an inverted letter L, with its lower portion prolonged. This 1 
hangs down into the leg-cavity beyond the median line. 4 
Crossing these organs obliquely, in the Nepidæ, lie the mus- _ 
cular fibers of the legs. The bands of muscle appear either 
straight or wavy, according as the legs are bent or extended, and 
remain perfectly quiet while the organs are beating. A careful 
study of the muscular system of the legs was first made, to avoid 
confusing it with the organs in question. With a power of 150 
diameters it can be made out very satisfactorily that the pulsatile 
organ is a thing separate from the muscular fibers of the leg, and | i 
does not involve them in its motion. This is best seen by focusing 
back and forth. When we have the muscles clearly in focus, the 
movements of the pulsating organ can still he seen lying a little a 
out of focus. In some of the thick-legged specimens, where a dis- 
