16 Psyche [February 
were made, the pulsations were rapid and irregular and for that 
reason difficult to count. A few attempts to determine the num- 
ber per minute gave the following results: 150, 124, 176,51. These 
must be taken as estimates only. Sometimes the pulsations would 
cease entirely in one leg for a number of seconds while continuing 
at the usual rate in the others. The periods of inactivity did not 
seem to be due to external stimuli. They occurred when the aphids 
were immersed in water or when placed on a dry depression slide. 
The movement of the dorsal heart was slower and of an entirely 
independent rhythm than that of the vessels. 
Pulsations were observed in the very youngest aphids found. 
But no action was detected in large embryos, even those with the 
leg muscles and external spines well developed. Apparently the 
vessels are not functional till birth. 
Locy has described the remarkable tenacity of these organs in 
the legs of Ranatra. In one case the vessel pulsated in an ampu- 
tated leg for a period of 26 hours and 20 minutes: Activity con- 
tinued even when sliced portions of the legs were used and when 
the vessel itself was cut in two, the posterior part still continued to 
pulsate. In contradistinction to this, the pulsatile vessels in the 
legs of Myzus persice ceased beating (except for a few sporadic 
twitchings) immediately upon the removal of the legs. They 
would not resume their activity when the legs were quickly placed 
in water or physiological salt solution. If the head were cut off or 
burned off with a hot needle, the pulsations stopped at once. 
Aphids which were immersed in an aqueous solution of nicotine 
sulphate (1 part of 40 per cent. nicotine sulphate by volume to 500 
parts of water), soon died and an immediate examination showed 
that the vessels in each leg had ceased to function. An injury 
from which the aphid finally partly recovered, such as a slight cut 
in the head, at first inhibited the action of the vessels, but with the 
recovery of the aphid, the vessels again resumed their normal rate of 
pulsation. 
From the above results, it is evident that there is a marked dif- 
ference in the reactions of the pulsatile vessels in Ranatra and 
Myzus persice under certain abnormal conditions. Accepting 
Ranatra as the more generalized type, we notice a radical change 
in the resistance of the pulsatile vessels to various kinds of injury 
as we pass directly from this to the more highly specialized aphid 
