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THE AUSTRALIAN NATURALIST. 105 
‘consider the breathing of an insect, which is effected, not 
through the mouth, but by means of small apertures (spira- 
cles) along the sides of the body, whence the air passes into 
.a wonderful system of delicate branching tubes (trachaea 
id § 
which extend throughout the body and appendages. Thus 
the air is, as it were, conveyed to the blood, not, as in man, 
the blood conveyed to the air of the lungs. All adult aquatic 
insects breathe exactly as land insects do, but many are the 
‘curious devices for obtaining air or carrying a supply of it 
below the surface of the water. It is in their larval (grub) 
- stages that water insects are more truly aquatic; some breathe 
.air direct by coming to the surface, others have developed 
tracheal gills and absorb air from the water. . It was ad- 
> vanced by Lord Avebury and others that probably primitive 
insects were all aquatic and breathed by gills, and that later 
they acquired the capacity of breathing by spiracles. There 
is, however, stronger evidence that the reverse is the case, 
viz.. that primitive insects were terrestrial, breathing by 
spiracles, and that aquatic habits were comparatively recently 
acquired ; acquired in most cases long after the wings were 
developed, and most of the great insect orders we are fami- 
ilar with had become differentiated. This view is supported 
by the fact that the more primitive present-day insects, such 
as Silver Fishes and Cockroaches, are not aquatic. Also, 
there is not a distinct order of aquatic insects, but aquatic 
habits have been acquired by members of widely different 
orders. Again, some aquatic larvae with gills show function- 
less spiracles, indicating priority for the spiracles and direct 
_ air breathing habits in these cases. 
Australia is rich in aquatic insects, and with two or 
three exceptions all types found elsewhere are recorded here. 
The knowledge of our own water insects, and more particu- 
larly of their habits, is very limited, and there is a large 
new field for even a novice in natural science who cares to 
carefully observe and accurately record the habits of Austra- 
lian water insects. These insects can be conveniently ob- 
_served by keeping them in glass jars of water with suitable 
aquatic plants growing in the water. 
Reviewing our species, we shall see how almost every 
Order of Insects is represented in the water. I give below 
-a list of the principal families of aquiatic insects recorded 
-from Australia :— : 
Order Cotxoprera (Beetles):—Fam. Dytiscidae (Carni- 
vorous Water Beetles), 154 species; Fam. Gyrinidae (Whirli- 
_gig Beetles), 20 species; Fam. Hydrophilidae (Water Beetles), 
. 21 species. Sg he 
Order Dirrera (Flies).—Fam. Culicidae (Mosquitoes), 
/36 species; Fam. Chironomidae (Midges), 100 species; Fam 
