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 obser\'ed 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. iVctivity 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 persicoe 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 persicoe 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 



