622 THE AMERICAN NATURALIST. (VoL. XXXV. 
Integument. — Drs. Hansen and Sorensen state, “As a 
peculiarity in Koenenia, we think right to emphasize at once 
that its skin is but slightly chitinized, especially on the abdo- 
men, where, consequently, there is no distinction between the 
(dorsal and ventral) plates and the pleura; so the expansion, 
which the abdomen must be capable of allowing, probably 
depends on the elasticity of this thin chitin itself." I think 
had these gentlemen attempted to section Koenenia they would 
not have been so emphatic about the thinness of its exoskele- 
ton. The chitinous cuticle, which rests on a delicate hypo- 
dermis, corresponds more nearly to that of most spiders, in 
that over the expanded abdomen it does not appear to form 
special plates. It also corresponds to spiders, in that it is a 
flexible or accordion-plaited covering, the folds of which run 
parallel with the long axis of the body. This arrangement 
thus allows of great expansion of the abdomen, its function 
being evidently the same as the folds in the late integument 
of the abdomen of Thelyphonus. Over the chelicerze labrum- 
hypostome and reproductive appendages the chitin is thick 
and yellow, while between the joints it is very thin. In the 
floor of the mouth the chitin is thrown into folds, running at 
right angles to the long axis of the body. This, in sagittal 
sections of the animal, gives it the appearance of possessing 
teeth. The entire chitinous surface of the animal is not 
smooth, but under high magnification appears to be covered 
with small dot-like elevations. 
Kenenia wheeleri is remarkable for the comparatively thick 
covering of hairs arising from its flexible cuticle. The smallest 
hairs are like down, covering the anterior surface of the labrum 
and the under surface of the hypostome. The longest and most 
delicate are the tactile hairs of the sixth, seventh, and eighth 
segments of the third pair of appendages. The broadest and 
heaviest spines are situated on the underside of the proxim 
joint of the chelicerz ; otherwise the setze are distributed as 
Dr. Wheeler has already shown. All the hairs over the body 
of Koenenia, with the exception of the tactile and the vor 
minute ones on the mouth appendages which are too delicate 
to be made out, are microscopically plumulose. 
