of books.

In general form Lepisma may be compared to the larva of Perla, a
net-veined Neuropterous insect, and also to the narrow-bodied species of
cockroaches, minus the wings. The body is long and narrow, covered with
rather coarse scales, and ends in three many jointed anal stylets, or
bristles, which closely resemble the many jointed antennae, which are
remarkably long and slender. The thermophilous species already alluded
to may be described as perhaps the type of the genus, the L. saccharina
being simpler in its structure. The body is narrow and flattened; the
basal joints of the legs being broad, flat and almost triangular, like
the same joints in the cockroaches. The legs consist of six joints, the
tarsal joints being large and two in number, and bearing a pair of
terminal curved claws. The three thoracic segments are of nearly equal
size, and the eight abdominal segments are also of similar size. The
tracheae are well developed, and may be readily seen in the legs. The end
of the rather long and weak abdomen is propped up by two or three pairs
of bristles, which are simple, not jointed, but moving freely at their
insertion; thus they take the place of legs, and remind one of the
abdominal legs of the Myriopods; and we shall see in certain other
genera (Machilis and Campodea) of the Bristle-tails that there are
actually two-jointed bristles arranged in pairs along the abdomen. They
may probably be directly compared with the abdominal legs of Myriopods.
Further study, however, of the homologies of these peculiar appendages,
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 Perla and Ephemera. The mode of
insertion of the antennae of this family is much like that of the
Myriopods, the front of the head being flattened, and concealing the
base of the antennae, 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. So in a
less degree does the head of the larvae 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,
carried far down on the under side of the head, the clypeus