312 
MR. NEWPORT ON THE TEMPERATURE OF INSECTS. 
but in none better than in the large Moths and Sphinges. When an insect has re- 
mained for some time in a state of repose, both the power and rate of pulsation are 
greatly diminished, but are again increased immediately the insect awakes. The 
manner in which the pulsation takes place, as seen through the delicate skin of the 
larva of the Puss Moth, Centra vinula, Steph., appears to be as follows : at the mo- 
ment the insect begins to awake there is a slight extension of the posterior segments 
of its body, followed immediately by a slight contraction of the same parts ; and al- 
most immediately afterwards there is an increased motion in the posterior part of the 
dorsal vessel, in the twelfth or penultimate segment, where the vessel is broadest, and 
as shown by Carus and Wagner, receives a current of blood which flows into it on 
either side. The contraction, or ventricular action of the vessel, commences first in 
this segment, and is gradually continued onwards through the chambers of the vessel 
in the preceding segments by a series of successive impulses, from behind forwards, 
communicated in succession by the valves in each chamber*, but which in the Cerura 
and Sphinx are not observed through the skin of the insect. These contractions force 
along the blood through the chambers of the heart in the ninth, eighth, seventh, sixth, 
and fifth segments with intermitted or pulsatory motion, so that while the middle and 
anterior chambers are contracting the posterior is again filling. The auricular, ex- 
panding, or receiving action of the vessel begins also in the twelfth segment, where, 
indeed, the greatest amount of blood seems to be received from the body, although it 
is also received by the other valves in the different segments. Immediately the poste- 
rior valve has impelled the blood onward to the next one, it begins again to expand. 
If the action of the vessel be carefully examined, the expansion and contractions of the 
chambers in the different segments in gradual succession from behind forwards, at 
every impulse, maybe readily observed. Each pulsation of the vessel is, I think, di- 
visible into three periods: first, the auricular, or filling, which is rather the longest; 
second, the ventricular ; and thirdly, the period of rest, which is immediately subse- 
quent to the ventricular, but is of rather shorter duration. From these causes the 
true arterial motion of the fluids through the thorax of the insect is later by one whole 
contraction of the vessel than in the posterior segment or division of the organ ; and 
it is also evident, on watching the motions of the vessel, that the period of rest is 
longer in the anterior or aortal portion of the vessel, which passes through the thorax, 
than in the posterior or true dorso-abdominal. It has been shown in other parts of 
this paper that after the insect has arrived at its full size as a larva there is a gradual 
diminution in its quantity of respiration and temperature ; and it is interesting to 
observe that this is coincident with a similar diminution both in its actual weight and 
in the pulsation of its dorsal vessel, and that the diminution continues until after the 
insect has changed to its pupa state, as shown in the accompanying Table. 
* See Bowerbank on Circulation of Insects, Entomological Mag. vol. i. p. 240. 
