394. 
stimulus applied to the body these sacs immediately con- 
tracted, and were thrown into tetanus by prolonged stimulus, 
as in Melolontha. These vessels seem therefore to behave 
somewhat like the small arteries in vertebrata, as seen in the 
rabbit’s ear or skin. The contractile vessels continue to con- 
tract feebly for a short time after the wing has been severed 
from the body, as is evidenced by a backward and forward 
motion of the blood-corpuscles when a wing possessing them is 
placed immediately after separation under the microscope. 
The blood-vessels of the wings of most insects which I 
examined (Blatta, Dytiscus, Hydrophilus, Melolontha) are 
infested with parasites, which attach themselves to the 
trachez, and always occur in greatest abundance in the main 
arterial trunks. ‘These parasites seem to differ considerably 
in each species. Fig. 2 is taken from a wing hardened in 
perosmic acid, which stains the parasites which are filled 
with oil-globules black. They therefore appear in the figure 
as dark elongated spots attached to the central trachea in the 
main artery (a). I hope shortly to make a communication 
to the Journal on the subject of these parasites. 
Blatta Orientalis casts its skin at certain periods, the chi- 
tinous investment splitting up the back, and the animal 
coming out, after several hours’ labour, quite soft and milk- 
white. I have as yet only been lucky enough to obtain 
one specimen, a female, in this state. The insects, when 
thus fresh from the old skin; are very transparent. Light 
may be thrown right through their bodies, and the action of 
the heart and valves observed to great advantage. A venous 
sinus surrounding the heart can be clearly seen, and also that 
the corpuscles within it move towards the posterior extremity 
of the body. Moreover, the blood may be seen entering the 
heart by side apertures from the sinus, and apparently leay- 
ing it by others. 
Although a good many fine trachez could be seen in the 
body quite distinctly, and though the power used was quite 
high enough to show corpuscles distinctly, no circulation 
taking place around these trachee was to be observed in the 
manner supposed by M. Blanchard. On account of the large 
size of the corpuscles, B. Orientalis is remarkably favorable for 
investigations of insect circulation. Unfortunately, these white 
insects rapidly—z. e. in a couple of hours—become so brown 
as to be no longer transparent, and rapidly become black.' 
1 Thinking it just within the limits of possibility that this brown colora- 
tion might be due to the presence of silver, I analysed one pound weight of 
Blatta ; I found no silver, but plenty of iron, and a remarkable quantity of 
manganese. 
