310 NEW YORK STATE MUSEUM 
tracheae by osmosis. Sanderson’s conclusions, to state them 
in another way, were that the paired dorsal cavities [pl.28, fig. 
4ndc] are connected with the exterior at the point ex, and that 
the wedge-shaped apical portion of the caudal spines can be 
shut down tightly on either side so as to close this opening, 
and that the air finds its way from the paired dorsal 
cavities through a tube into the paired ventral cavities and 
thence is carried along this cavity to the tracheal system. 
From my own studies I have been led to conclude that there is 
never a natural opening leading into the paired dorsal cavities, 
and that, when there is such an opening present, it is an artifact. 
The cuticle at this point is thin and easily broken, while the 
cavity is lined with hypodermal cells; and I do not know of 
such a condition existing anywhere among the Hexapoda where 
there is a cavity opening to the exterior and lined by an epithe- 
lium. It is true that the mouth and rectal openings are lined 
with epithelium, but in both of these cases the lumen end of 
the cells is covered by a well marked cuticle. In addition to 
the above, I have found that the wedge-shaped portion is always 
rigid and not capable of any motion, while any air that might 
find its way into the paired ventral cavities, if an opening did 
exist, would be unable to reach the tracheal system, because 
the base of this cavity is completely plugged up by a portion 
of the cuticular pocket, as has already been described [pl.28, 
fig.8w and fig.6pve]. I have been unable to find any tubes such 
as Mr Sanderson describes, while his so called elliptical open- 
ings are not openings but areas in the cuticle, that are very thin 
and transparent and very liable to lead one into error if one 
worked only with thick free-hand sections. When the caudal 
spines are mounted in Canada balsam, so that their dorsal 
surface can be studied, two rows of these elliptical openings can 
be seen forming the ectal surface of apparently well marked 
grooves or furrows, but these grooves or furrows are nothing 
more than the cavities of the paired dorsal cavities into which 
one looks through the transparent outer cuticle. This is further 
confirmed by the study of cross sections of the caudal spines; 
