ue THE INSECT WORLD. 
The anterior or aortic portion of the dorsal vessel shows neither 
fan-shaped lateral expansions, nor orifices, and consists of a single 
membranous tube. On reaching the interior of the head it opens 
in the lacunary inter-organic system. The whole of the blood set 
in motion by the contractions of the cardial portion of the dorsal 
vessel runs into the cavity of the head, and circulates afterwards 
in irregular channels formed by the empty spaces left between 
the different organs. It is the unoccupied portions of the great 
visceral cavity which serve as conductors to the blood, and 
through them run the main currents that one sees in the lateral 
and lower parts of the body, whence these currents regain the 
back part of the abdomen, and enter the heart after having 
traversed externally the different organs they encountered. 
These principal channels are in continuity with other gaps pro- 
vided between the muscles, or between the bundles of fibres of 
which these muscles are composed, or else in the interior of the 
intestines. 
The principal currents send into the network thus formed minor 
branches, which, having ramified in their turn among the prin- 
cipal parts of the organism, re-enter some main current to regain 
the dorsal vessel. 
In the transparent parts of the body the blood may be seen 
circulating in this way in a number of inter-organic channels, 
more or less obvious, penetrating the limbs, overspreading the 
wings, when these appendages are not horny, and, in short, dif- 
fusing itself everywhere. ‘‘ If, by means of coloured injections,” 
says M. Milne Edwards, “ one studies the connections which exist 
between the cavities in which sanguineous currents have been 
found to exist, and the rest of the economy, it is easy to see that 
the irrigatory system thus formed penetrates to the full depth of 
every organ, and should cause the rapid renewal of the nourishing 
fluid in all the parts where the process of vitality renders the 
passage of this fluid necessary.” 
We shall see presently, in speaking of respiration, that the 
relations between the nourishing fluid and the atmospheric air are 
more direct and regular than was for a long time supposed. 
In short, insects possess an active circulation, although we find 
neither arteries nor veins; and although the blood put in motion 
