Class of the Honey-Bee. 23 
lowest, simplest, Protozoan branch, which includes ani- 
mals often so minute that we owe our very knowledge of 
them to the microscope, and so simple that they have been 
regarded as the bond which unites plants with animals. 
THE CLASS OF THE HONEY-BEE. 
Our subject belongs to the class Insecta, which is mainly 
characterized by breathing air usually through a very com- 
plicated system of air tubes. These tubes (Fig. 1), which 
are constantly branching, and almost infinite in number, 
Fic. 1. 
A Trachea, magnified. 
a 
are very peculiar in their structure. They are composed of 
a spiral thread, and thus resemble a hollow cylinder formed 
by closely winding a fine wire spirally about a rod, so as to 
cover it, and then withdrawing the latter, leaving. the wire 
unmoved. This spiral elastic thread, like the rings of car- 
tilage in our own trachea, serves to make the tubes rigid; 
and like our trachea—wind-pipe—so these trache or air- 
tubes in insects are lined within and covered without by a 
thin membrane. Nothing is more surprising and interest- 
ing than this labyrinth of beautiful tubes, as seen in dis- 
‘ secting a bee under the microscope. I have frequently 
detected myself taking long pauses, in making dissections 
of the honey-bee, as my attention would be fixed in admi- 
ration of this beautiful breathing apparatus. In the bee 
these tubes expand in large lung-like sacs (Fig. 2, f), one 
on each side of the body. ‘Doubtless some of my readers 
have associated the quick movements and,surprising activ- 
ity of birds and most mammals with their well developed 
