* 130 NATURAL HISTORY OF WASPS. 
the air is applied to the renovation of the blood. 
And, generally speaking, the relations between the 
respiration and circulation in insects are just the 
reverse of those which obtain in warm-blooded 
animals with heart and lungs. These differences 
will all appear as we successively examine the dif- 
ferent portions of the respiratory system, 
The respiratory movements may be observed very 
easily in any wasp that will stand still. The upper 
surface of the abdomen is alternately lengthened 
and retracted, and the air follows these movements 
through the spiracles. If we place a wasp in a live- 
box, under a low power of the microscope, we may 
observe an alternate undulatory expansion and con- 
traction of the large air-vesicles between the first 
and second ventral scales. A very gentle compres- 
sion must be used, only just enough to steady the 
insect under examination, or the motion will be 
interrupted. The number of respirations in ‘a minute 
varies, as in the higher animals, with the amount of 
labour which they may have recently undergone, or 
the degree of present excitement. In the honey-bee 
the number varied from eighty to one hundred and 
sixty, as observed by Mr. Newport,* and in some 
insects of this order the number was even higher. 
The stigmata, or external orifices of the respiratory 
apparatus in this segment of the body, lie in a row 
on each side, one at either end of each dorsal scale. 
They are to be looked for in the black part, where it 
overlaps the ventral scale, and is itself overlapped by 
the preceding rmg when the abdomen is contracted. 
To the unassisted eye they appear merely as minute 
* ¢ Cyclopedia of Anatomy and Physiology,’ Vol. II, p. 988. 
