395 
A ready method for injecting the circulatory system of in- 
sects has long been a desideratum. ‘The injection from the 
heart is beset with many difficulties, owing to its brittleness, 
and has led, as yet, to no certain conclusions, the connec- 
tion of the large afferent and efferent blood-vessels in the 
wings with the heart being still uncertain. It may be well 
here to add a short account of a method which, I believe, 
may be of much assistance in clearing up such points as 
these, and which may also yield some interesting physiolo- 
gical results. 
When the fore wing of a large living Coleopterous insect 
(Dytiscus marginalis, Hydrophilus piceus, and Melolontha vul- 
garis, e. g.) is cut transversely in two with scissors, a row of 
blood drops may be seen along the edge of the cut, which pro- 
ceed from the large vessels divided by the operation. At the 
front border or costa of the wing this bleeding is most profuse, 
since the largest artery occupies this position. At this spot 
a very fine-drawn-out glass tube can easily be introduced 
either into the half of the wing still attached to the body, or 
the corresponding half which has been cut away. I have 
found it most convenient to use as a pressure apparatus a 
simple short india-rubber tube filled with injecting fluid, 
having the canula at one end and stopped at the other. By 
pressure with the finger on the tube the fluid may readily 
be forced into the vessels. If the wing of Dytiscus marginalis 
be thus injected with indigo-carmine (which I have found to 
run best) or Berlin blue solution, a very beautiful prepara- 
tion is obtained. 
By injecting the other half of the wing in the direction of 
the body the heart may readily be filled. When an insect 
(Cockchafer or Dytiscus) has thus its blood-system filled 
with indigo-carmine, this pigment is rapidly excreted by 
means of the kidney tubes, just as is the case when the same 
experiment is made on mammals, as in Crzonzwesky’s ex- 
periments. Basch has shown that the kidneys in Blatta 
Orientalis contain uric acid. ‘This observation tends to show 
a further identity of function between these organs and the 
mammalian kidneys. ‘The excretion takes place very rapidly, 
the tubes in Blatta Orientalis being fillea with blue pigment 
a few hours after its injection into the heart. In Hydrophilus 
piceus a series of simple circular glands, with which the in- 
testinal wall is crowded, also excrete this pigment ; nearly the 
whole intestine, shortly after the injection of the indigo- 
carmine, becomes blue, and on microscopic examination the 
pigment is found collected in the lumen of these glands. 
