192 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
beetle, ITydrophilus piceus. The results of my investigations were after- 
wards published in Paris. 2 " A few months later Graber also described 
the structure of the tracheae, pointing out Leydig's error. Graber's ob- 
servations are published incidentally in his article on the tympanal 
organs of the Oi tlioptera. 245 
I have found that the account 1 I lien published of the minute anatomy 
of the air tubes in Ilydrophilus is applicable, almost without change, to 
the grasshoppers, and I have, moreover, been able to convince myself 
that the epithelium is not columnar, but a true pavement epithelium 
(Pflasterepithel) as I had previously found it to be in llydrophilus and 
other insects. My own observations certainly imply that Dr. Chun is 
in error as to the nature of this layer in those species that he examined. 
In order to avoid repetition I reproduce here a figure (7) of a longitudi- 
nal section of a trachea of the European water beetle, taken from the 
American Nattvralist, -July, 1877. Externally lies the 
epithelium cp, which is readily recognized by the flat- 
tened elongated nuclei. Next follows the inner layer of 
the cuticula, cw, and interiorly the darker colored inner 
layer, in which are imbedded the dark colored spiral fila- 
ments/. This arrangement recurs in a number of in- 
sects and probably in all, the variations being merely 
in the proportionate thicknesses of the various parts, 
and the relative size of the spiral threads. 
If short pieces of the tracheae be pulled out, then 
stained with carmine or haematoxiline and mounted, it 
section ot ? large De noticed that the size of the spiral filaments, and 
trachea of Hydro- also the distance between them, diminishes with the 
phiius piceus. s j ze of the tracheae. Where a smaller trachea springs 
from a larger one, there is not a gradual passage from the large to the 
small threads, but at the point of origin the filaments of the large 
tracheae bend apart so as to leave a space in which the tracheal branch 
takes rise, beginning at once with small spiral threads. 
The preparations we are now considering further show that there is 
not a single spiral thread, but several, which run parallel to one another, 
as I have shown before 246 , and end after making a few turns around the 
trachea. The single threads terminate not abruptly but by tapering 
down to a point and so disappearing. 
The nuclei (Figs. 8 and 61) of the tracheal epithelium are elliptical in 
outline, much flattened, though considerably thicker than the body of 
the cells. Their long axis is more or less nearly parallel with that of the 
trachea, and they all have a very distinct and highly refringent nucleo- 
lus ; sometimes two. The nucleoli are, I bebeve, always eccentrically 
144 Archives de Physiologia Normals et Pathologique, 1876, p. 1, and in Ranvier's Travaux do. Labora- 
toire, etc., 1876, p. 1. 
145 Graber : Denk. Wien. Akad, T xx vi, p. 35. 
Minot: Recherch.es histologiques sur les Trach6es de l'Hydrophilus picous. Arch, de PhysioL 
expt. 1876, p. 1. 
