314 
MR. NEWPORT ON THE TEMPERATURE OF INSECTS. 
(luring- the first and second periods of the larva state, or before it has entered its third 
skin, and when its weight is no more at most than two thirds of a grain. From not 
knowing the temperature of the atmosphere at the period of making the observations 
on this insect in its second skin, I am doubtful whether the rate of pulsation be not 
in reality greatest during the earlier life of the larva, before it has thrown off its first 
skin, because this was really the case in all the observations, if we except only two 
which were made on the afternoon of the same day, when the larva was at about the 
age of two hundred and seventeen hours. These observations being excepted, it will 
be seen from Table IX. that the rate of pulsation is gradually diminished from the 
earliest period of the larva state until the insect has changed into a pupa, — that while 
the rate of pulsation within % few hours after the insect has left the egg varies from 
seventy- five to ninety, and in its second skin, or at an average age of about two hun- 
dred and forty hours, it is but very little lower, it becomes in its third reduced to an 
average of seventy-five, in its fourth to less than sixty, in the middle period of its 
fifth to a maximum of fifty-five, and the latter period of the same to scarcely more 
than thirty-two pulsations per minute. These are interesting facts as connected with 
the power which the insect possesses of generating heat. It is, as before stated, at 
about the middle period of its fifth state or condition as a larva, when it is feeding 
most voraciously, that the insect is able to generate the greatest amount of heat. 
Although it will be seen from the additional facts about to be stated that both during 
sleeping and activity, when most vigorous as a larva, as also when passing into the 
enfeebled condition of a pupa, there is a coincident and correspondent activity or 
diminution in the rate of pulsation with the increase of motion, respiration, or diges- 
tion ; yet the primary source of the development of heat is not dependent upon the 
velocity or rapidity of the circulation, since the period in which there is the greatest 
rapidity of circulation is that in which the larva is least able to generate and maintain 
its greatest amount of temperature. Another circumstance which tends greatly to 
prove that the amount of heat does not necessarily depend upon the rapidity of the 
circulation is the different rates of pulsation when the insect is placed in different tem- 
peratures, or when in different states of health in the same temperature. In the first 
case the rate of pulsation may be very considerably increased, while the amount of tem- 
perature remains nearly, or perhaps exactly the same. In the latter instance the tempe- 
rature may continue exactly the same, but the rate of pulsation be diminished. Thus 
in two specimens of Sphinx ligustri which were both of the same age, and in similar 
conditions of activity, feeding in the same atmospheric temperature, when the obser- 
vations were made upon both at the same time, the temperature of the insects was 
exactly the same, '9 above that, of the atmosphere, but the rate of pulsation in one 
specimen, which was perfectly healthy, was forty-one beats per minute ; while in the 
other, which was unhealthy, it was only thirty-eight. 
