306 NEW YORK STATE MUSEUM 
ooze and yet have none of those structures common to insects 
that would fit them for such a mode of life. What to the 
writer has been the most interesting phase of this investiga- 
tion has been the determination of how these insects are able 
to obtain a supply of air. The most casual observers have 
noticed in walking over swampy places where there is an 
abundance of submerged vegetation that at each step great 
quantities of bubbles rise to the surface. These bubbles come in 
part from the crushed stems of the plants that have been trod on 
and are an ocular demonstration of the abundant air supply held 
by such plants. If one of the stems of an aquatic plant as Sagit- 
taria be taken and sectioned transversely [p1.24, fig.1] we shall 
find that it is made up of a great quantity of small cells arranged 
in the form of anastomosing rings inclosing large spaces, and 
that fully two thirds of the area of the section is occupied by 
these spaces. Now, if another stem is sectioned longitudinally 
[pl.24, fig.2], we shall find that the cells are arranged 
in parallel rows with delicate cross' walls dividing the 
longitudinal spaces into areas three or four times as 
long as broad. Each of these spaces is filled with air, and 
it is on such a supply that the larvae and pupae of Donacia 
depend. The larvae tap the air supply locked up in the stems 
of aquatic plants by pushing their caudal spines through the 
epidermis of the plant and rupturing the cells surrounding the 
alr spaces. The air contained by such plants is of about the 
Same richness in oxygen as the surrounding atmosphere. 
When the tissue of the plant is ruptured, the inclosed air, be- 
ing lighter than the water, moves to the outer surface of the 
plant, and, if there were nothing to collect it, it would pass on 
to the surface of the water. But the spiracular openings be- 
ing at the immediate base of the spines [pl.27, fig.19s] and 
the larva holding the apex of its abdomen close to the surface 
of the plant, the air is collected before it can escape into the 
water. Plate 28, figure 1, shows the apical portion of a grow- 
ing stem with a larva with its caudal spines inserted into the 
tissues of a plant and in the act of respiring. On the many 
