BRISTLE-TAILS AND SPRING-TAILS. 93 
and especially a knowledge of the embryological development of 
Lepisma and Machilis, is needed before this interesting point can 
be definitely settled. The three many-jointed anal stylets may, 
however, be directly compared with the similar appendages of Per- 
la and Ephemera.. The mode of insertion of the antennz of this 
family is much like that of the Myriapods, the front of the head be- 
ing flattened, and concealing the base of the antennæ, as in the 
Centipedes and Pauropus. Indeed the head of any Thysanurous 
insect seen from above, bears a general resemblance in some of its 
features to that of the Centipede and its allies. Soin a less degree 
does the head of the larve of certain Neuroptera and Coleoptera. 
The eyes are compound, the single facets forming a sort of heap. 
The clypeus and labrum, or upper lip, is, in all the Thysanura, car- 
ried far down on the under side of the head, the clypeus being 
almost obsolete in the Poduride, this being one of the most essen- 
tial characters of that family. Indeed, it is somewhat singular 
that these and other important characteristics of this group have 
been’ almost entirely passed over by authors, who- Fig. 93. 
slight and inconsiderable characters. The mouth- 
parts of the Lepismatide (especially the thermoph- 
ilous “Lepisma, which we now describe) are most 
readily compared with those of the larva of Perla. 
The rather large, stout mandibles are concealed at their tips, 
under the upper lip, which moves freely up and down when the 
creature opens its mouth. The mandible is about one third as 
broad as long, armed with three sharp teeth on the outer edge, 
and with a broad cutting edge within, and still further within, a 
lot of straggling spinules. In all these particulars, the mandible 
of Lepisma is comparable with that of certain Coleoptera and 
Neuroptera. So also are the maxille and labium, though we are 
not aware that any one has indicated how close the homology 
is. The accompanying figure (23) of the maxilla of a beetle 
may serve as an example of the maxilla of the Coleoptera, Or- 
thoptera, and Neuroptera. In these insects it consists invari- 
ably of three lobes, the outer being the palpus, the middle lobe 
the galea, and the innermost the lacinia; the latter undergoing the 
greatest modifications, forming a comb composed of spines and 
hairs varying greatly in relative size and length. How much the: 
