ANATOMY AND PHYSIOLOGY. 131 
depressions, or pin-hole apertures. But, by the aid 
of the microscope, these holes are shown to have a 
crescentic or kidney-shaped outline, with a distinct 
raised edge round them. They communicate directly 
with the spiracles, and through them, by means of a 
short tube, with the great lateral air-trunks. 
The thoracic spiracles of the wasp are larger than 
the abdominal, and seem to be her chief vocal 
organs. But the abdominal spiracles are more easily 
displayed, by reason of the looser structure of the 
surrounding parts and of the thinner integument in 
which they are placed. So we shall do well to begin 
with these, and, on account of her larger size, make 
the hornet the subject of our examination. The 
readiest way to prepare them is to remove the por- 
tion of the scale which contains them, dry well, soak 
in turpentine to make them transparent, and mount 
at once in Canada balsam. We shall require at least a 
quarter-inch object glass for the study of their details. 
Beginning from the outer surface, we find that the 
horny rig which surrounds the stigma is thicker on 
the concave—as presented to the aperture—than on 
the convex margin. That is a thick rim: this is 
thinner, and gives origin to a broad membranous 
tongue, seen best from the outer side, which stretches 
nearly all across the opening of the stigma. Ad- 
justing the focus so as to see deeper into the prepara- 
tion, or turning the object over, we find a strong, 
rough membrane to arise from the inner surface of 
the thick concave rim of the stigma, forming a pouch, 
shaped like the letter D. A light, horny slip marks 
the line where the edge of this membrane seems to 
join on to the trachea. One end of this slip is turned 
K 2 
