BRISTLE-TAILS AND SPRING-TAILS. 99 
Peabody Academy, affording ample material for study until nearly 
Christmas time, and again, late in February. About, a hundred 
species are found in Europe, and nearly a quarter of that number 
I have, with the aid of my friend Mr. C. A. Walker, observed in 
this country, though paying little attention to them previous to 
last autumn. ; 
The body of the Poduras is rather short and thick, most so in 
Smynthurus (Fig. 26), and becoming long and slender in Tomo- 
cerus and Isotoma. The segments are inclined to be of unequal 
size, the prothoracic ring sometimes becoming almost obsolete, and 
some of the abdominal rings are much smaller than others; while 
in Anura and Lipura, the lowest forms of the group, the seg- 
ments are all much alike in size. 
The head is, in form, much like that of certain larvee of Neurop- 
tera. The basal half of the head is marked off from the eye-bear- 
ing piece (epicranium) by a V-shaped suture (Fig. 28, head of 
Degeeria), and the insertion of the antenne is removed far down 
the front, near the mouth, the clypeus being very short; this 
piece, so large and prominent in the higher insects, is not distinct- 
ly separated by suture from the surrounding parts of the head, 
thus affording one of the best distinctive characters of the Podu- 
ride. The eyes are situated on top of the head just behind the 
antennæ, and are simple, consisting of a group of from five to eight 
or ten united into a mass in Smynthurus, but separated in the Po- 
duride (Fig. 41, e, eye of Anura). The antenne are usually 
four-jointed, and vary in length in the different genera. The 
mouth-parts are very difficult to make out, but by soaking the in- 
sect in potash for twenty-four hours, thus rendering the body 
transparent, they can be satisfactorily observed. They are con- 
structed on the same general type as the mouth-parts of the Neu- 
roptera, Orthoptera, and Coleoptera, and except in being degraded, 
and with certain parts obsolete, they do not essentially differ. On 
observing the living Podura, the mouth seems a simple ring, with a 
minute labrum and groups of hairs and spinules, which the ob- 
server, partly by guess-work, can identify as jaws, and maxilla, 
and labium. But in studying the parts rendered transparent, we 
can identify the different appendages. Fig. 29 shows the common 
Tomocerus plumbeus greatly enlarged, and as. the mouth-parts of 
the whole group of Poduras are remarkably constant, a description 
of one genus will suffice for all. The labrum, or upper lip, is sepa- 
