380 The American Naturalist. [May, 
THYSANURA. 
“ Entomobrya cavicola Banks. Nov. sp. (Plate X, Fig. 2.) 
“Length 2mm. Whitish hyaline, intestine showing through 
darker; clothed with rather long scattered bristles and finer, 
shorter hairs; head not broader at tip in side view; no eyes; 
antennz one-third longer than the head, first joint very short, 
second twice as long, third shorter, fourth longest; legs short, 
two claws at tips; mesothorax no longer than metathorax ; 
first abdominal segment indistinct, fourth longer than third 
or second, fifth apparently entire, blunt at tip; furcula rather 
slender, mucrones curved. Several specimens. Mammoth 
Cave, Kentucky.” (Banks.) 
This minute species occurs in very great numbers in a 1 single 
locality, a side avenue which leads over the narrow passage 
called the Labyrinth to the top of Gorin’s Dome, in the older 
portion of the cave. In collecting it I had to lie on my face 
with the lamp close to the ground, and on turning over a frag- 
ment of an old wheel-barrow, that had been in the cave for two 
score or more years, and was so rotten that slight effort only 
was needed to tear it to bits, these little insects would be seen 
running about in every possible direction and in great haste. ` 
They were both on the under surface of the fragments of wood 
and also on the earth under them in equal numbers; when dis- 
turbed in the attempt to secure them the characteristic jump- 
ing movement of the group availed here to make collection 
difficult. It was noticed that many of them in springing up 
in the air would rise to an extraordinary height for so small 
an insect, frequently two or even three inches from the board. 
Others would land in nearly the same place as that from which 
they started, having a kind of boomerang movement that was, 
at least, curious. A paper bag would have secured hundreds 
by taking stick and all; but, as is usual on such occasions, the 
paper bag was not at hand. It is interesting to note, that while 
they represented a generation that must have been along way 
from their beginning in the cave, introduced, of course, from 
the outside world originally, they still retained the habits of 
their earlier ancestors and of the group, and sought, in the 
