506 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 [pi. 24, fig.l] 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.2-i, flg.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 

 air 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.l9s] 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 ^ 



