262 CLASS VIII. 
conclude from hence that the circulation of blood is unnecessary in 
Insects, and consequently does not exist. The circulation of blood 
has not respect to respiration alone, it is not merely for the con- 
version of venous blood into arterial; it is necessary that arterial 
blood should circulate that it may serve for nutrition and secretion. 
Many Insects live in water: but of these the greater number 
breathe atmospheric air; like whales amongst mammals some come 
to the surface of the water for that purpose. But usually there are 
special arrangements for conducting the air, so that the Insect can 
remain under water. This is seen ea. gr. in the larve of Diptera, 
which live under water; those of Culex have at the posterior 
part of the body a lateral canal with fine hairs at the orifice; the 
larvee of Stratiomys have a canal at the end of the abdomen, whose 
orifice is fringed with a circlet of plumose hairs; the genera Nepa 
and Ranatra have a tail composed of two filaments at whose base 
are two air-slits!. These water-insects die in a few hours if the air 
has no access to the water. Other Insects breathe in the water itself, 
that is, they breathe the air that is diffused through the water, as 
fishes do by their gills. Such Insects have no air-slits: the air 
must therefore penetrate the walls of the tracheew, which to that 
end are spread out either in filiform or capillary appendages (in the 
larve of Gyrinus, of Semblis, the nymphe ot Chironomus) or in 
leaf-like plates at one side of the body (Ephemera), or at the 
extremity of the abdomen (Agrion). These parts have been termed 
Gills’; they are not found in perfect Insects. Gills of this sort, 
from which blind air-tubes arise, occur in the rectum of the larva 
of Libellula as five rows of plumose incised leaflets. From them 
arise six longitudinal stems, of which two, larger than the rest, 
uniwersum corpus disperguntur, sic ut singule partes aeris particulas per pulmones et 
sanguinis portiones per arterias recipiat.” MALPIGHI Anatome plantarum, Op. om. I. 
ps. 
1 Figures of Culex in SWAMMERDAM, Bibl. nat. Tab, XXXI. figs. 4, 5; of Stratiomys, 
ibid. Tab. XXXIx.; of Nepa, in Durour, 1.1. The abdomen of Nepa and Ranatra 
has besides three pair of conspicuous, but closed, air-slits, in which very large branches 
of air-tubes terminate with blind ends. 
2 This nomenclature is only in part correct. The proper respiratory organs of 
Insects, the air-tubes, belong to the category of lungs, whether the air penetrates by 
external apertures (stigmata), or the tubes be filled with air from endosmotic action. 
The air in fact is in the inside, and the stream of blood (along the trachez) on the 
outside, and this relation is just the reverse of that which prevails in gills. 
