* 146 NATURAL HISTORY OF WASPS. 
veloped, fade away with the greater development of 
the respiratory system in the perfect insect. For 
now, he says, the air comes to the blood, instead of 
the blood having to go im search of the air. To obtain 
a view of the central trunk we must spread out the 
dorsal scales in one piece, previously cleared of all 
the abdominal viscera, and having only the lining of 
fatty tissue lymg on them. If the specimen thus 
prepared and pinned out under water be examined in 
a good light, we shall observe a transparent line 
running down the middle, clearer and more trans- 
parent as the specimen is more recent. This is 
the heart, the mam trunk of the circulation. 
Now, with a bent needle carefully scrape off this 
fatty lining of the scales, gathering it all up, heart 
and all, into a flake. By drawing on this, a long 
tube may often be extracted from the thorax and 
head, even up to the bifurcation of the vessel. By 
careful manipulation, alternately teasing and pressing 
this mass under water, much of the fatty matter 
may be removed, and the parts may be arranged for 
examination in glycerme, as a transparent object, 
under the microscope. The abdominal portion will 
now be seen to consist of a central tube, interrupted 
at regular intervals by a series of valves which are 
formed by a small piece of the tube bemg drawn in,— 
intus-suscepted, as anatomists call it—like the foot of a 
stocking. On either side of each of these internodes 
is a triangular strap of muscle tapering off to a point 
which is inserted into the corresponding dorsal scale. 
At the pomt of the strap the fibres are undistin- 
guishable from those of ordinary voluntary muscle, 
but as the band spreads out to cover the vessel they 
—— ee. 
