BRISTLE-TAILS AND SPRING-TAILS. 101 
Another organ, and one which, so far as I am aware, has been 
overlooked by previous observers, I am disposed to consider as an 
ovipositor. In the genus Achorutes, it may be found in the seg- 
ment just behind the spring-bearing segment, and situated on the 
median line of the body. It consists (Fig. 36) of two squarish 
valves, from between which project a pair of minute tubercles, or 
blades, with four rounded teeth on the under side. This pair of 
infinitesimal saws, remind one of the blades of the saw-fly, and I 
am at a loss what their use can be unless to cut and pierce so as to 
scoop out a place in which to deposit an egg. It is homologous in 
situation with the middle pair of blades which compose the oviposi- 
tor of higher insects, and if it should prove to be used by the 
creature in laying its eggs, we should then have with the spring, 
an additional point of resemblance to the Neuroptera and higher 
insects, and instead of this spring being an important differential 
character, separating the Thysanura from other insects, it binds 
them still closer, though still differing greatly in representing only 
a part of the ovipositor of the higher insects. 
But all the Poduras differ from other insects in possessing a re- 
markable organ situated on the basal segment of the abdomen. 
It is a small tubercle, with chitinous walls, forming two valves 
from between which is forced out a fleshy sucker, or, as in Smyn- 
thurus, ‘a pair of long tubes, which are capable of being darted 
out on each side of the body, enabling the insect to attach itself — 
to smooth surfaces, and rest in an inverted position. 
The eggs are laid few in number, either singly or several to- 
gether, on the under side of stones, chips, or, as in the case of Ts- 
otoma Walkerii Pack., under the bark of trees. They are round, 
transparent. The development of the embryo of Isotoma in gen- 
eral accords with that of the Phryganeide and suggests the near 
relationship of the Thysanura to the Neuroptera. 
Sir John Lubbock has given us an admirable account of the in- 
ternal anatomy of these little creatures, his elaborate and patient 
dissections filling a great gap in our knowledge of their internal 
structure. The space at our disposal only permits us to speak 
briefly of the respiratory system. Lubbock found a simple sys- 
tem of tracheze in Smynthurus which opens by “ two spiracles in 
the head, opposite the insertion of the antenne,” i. e., on the 
back of the head. (Von Olfers says, they open on the prothorax.) 
Nicolet and Olfers claim to have found tracheæ in several lower 
