356 Anatomy and Physiology of the Family Nepide. [ 
epithelial layer composed of five-sided cells, each containing 
prominent central nucleus. In some cases two nuclei are pr 
When these insects are irritated, a secretion is freely thrown € 
around the base of the beak, which produces death very quick 
when introduced on a needle point into the body of an insect. 
“cephalic glands” may be the source of this poisonous secrel 
on the other hand their function may be entirely different; 
question may be decided by the chemical analysis of the sect 
of these glands, that is now being made in the University of Midi 
igan. 
II. THE CIRCULATORY SYSTEM. 
After the food is reduced to chyle in the alimentary can 
passes by osmosis through the walls of the intestines into 
general circulation; it is conveyed in this way to various pars 
the body, and converted into tissue. The. circulation a 
blood and the structure of the heart in insects is constet 
of the most difficult points in their physiology, on account 3 
delicacy of the structure involved, and the confusion that 
arisen among authorities from the absence of true arem 
i i i is attached to this 
veins. So much interest and importance 1s a 
ject, that I give below a brief history of it. — 
About the middle of the seventeenth century Sw Hi 
and Malpighi, each independently, discovered in the 
tain insects a rhythmically contracting vessel lying l 
back, which they considered a heart. In the cour 
Lyonet threw some doubt upon this conclusion in his 
work on the larva of Cossus ligniperda. This doubt "o 
by Cuvier, who, after a special study of circulation F 
as his opinion that no such thing as a regular ae 
in this class of animals. Thus naturalists came to ©" ” 
sects had no circulation. | 
In the early of the present centu : 
the true Panay of the circulation of blood ga 
his proof was too strong to admit of question. > Jot 
aid of his microscope, in a small transparent ee 
the heart, circulate through the limbs, wings ® 
return to its starting point, thus tracing the pe ae 
His results were published in the year 1827, 48" ” 
firmed by other naturalists. m L 
In studying this subject in the Nepide, + y 
an 
ire LE 
ry, however, 
