BRISTLE-TAILS AND SPRING-TAILS.
The Thysanura, as the Poduras and their allies, the Lepismas, are
called, have been generally neglected by entomologists, and but few
naturalists have paid special attention to them.[9] Of all those
microscopists who have examined Podura scales as test objects, we wonder
how many really know what a Podura is?
In preparing the following account I have been under constant
indebtedness to the admirable and exhaustive papers of Sir John Lubbock,
in the London "Linnæan Transactions" (vols. 23, 26 and 27).
Entomologists will be glad to learn that he is shortly going to press
with a volume on the Poduras, which, in distinction from the Lepismas,
to which he restricts the term Thysanura, he calls Collembola, in
allusion to the sucker-like tubercle situated on the under side of the
body, which no other insects are known to possess.
The group of Bristle-tails, as we would dub the Lepismas in distinction
from the Spring-tails, we will first consider. They are abundant in the
Middle States under stones and leaves in forests, and northward are
common in damp houses, while one beautiful species that we have never
noticed elsewhere, is our "cricket on the hearth," abounding in the
chinks and crannies of the range of our house, and also in closets,
where it feeds on sugar, etc., and comes out like cockroaches, at night,
shunning the light. Like the cockroaches, which it vaguely resembles in
form, this species loves hot and dry localities, in distinction from the
others which seek moisture as well as darkness. By some they are called
"silver witches," and as they dart off, when disturbed, like a streak of
light, their bodies being coated in a suit of shining mail, which the
arrangement of the scales resembles, they have really a weird and
ghostly look.
The most complicated genus, and the one which stands at the head of the
family, is Machilis, one species of which lives in the Northern and
Middle States, and another in Oregon. They affect damp places, living
under leaves and stones. They all have rounded, highly arched bodies,
and large compound eyes, the two being united together. The maxillary
palpi are greatly developed, but the chief characteristics are the
two-jointed stylets arranged in nine pairs along each side of the
abdomen, reminding us of the abdominal legs of Myriopods. The body ends
in three long bristles, as in Lepisma.
The Lepisma saccharina of Linnæus, if, as is probable, that is the name
of our common species, is not uncommon in old damp houses, where it has
the habits of the cockroach, eating cloths, tapestry, silken trimmings
of furniture, and doing occasional damage to libraries by devouring the
paste, and eating holes in the leaves and covers 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 antennæ, 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
tracheæ 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 antennæ of this family is much like that of the
Myriopods, the front of the head being 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. So in a
less degree does the head of the larvæ 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 being almost
obsolete in the Poduridæ, this being one of the most essential
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 have consequently separated these
insects from other groups on what appear to the writer as comparatively
slight and inconsiderable characters. The mouth-parts of the Lepismatidæ
(especially the thermophilous 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
inwards 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 maxillæ and labium, though we are not aware
that any one has indicated how close the homology is. The accompanying
figure (152) of the maxilla of a beetle may serve as an example of the
maxilla of the Coleoptera, Orthoptera and Neuroptera. In these insects
it consists almost invariably 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 palpi vary in these groups of insects is well known. The galea
sometimes forms a palpus-like appendage. Now these three lobes may be
easily distinguished in the maxilla of Lepisma. The palpus instead of
being directed forward, as in the insects mentioned above (in the pupa
of Ephemera the maxilla is much like that of Lepisma), is inserted
nearer the base than usual and thrown off at right angles to the
maxilla, so that it is stretched out like a leg, and in moving about the
insect uses its maxillæ partly as supports for its head. They are very
long and large, and five or six-jointed. The galea, or middle division,
forms a simple lobe, while the lacinia has two large chitinous teeth on
the inner edge, and internally four or five hairs arising from a thin
edge.
[Illustration: 152. Maxilla.]
The labium is much as in that of Perla, being broad and short, with a
distinct median suture, indicating its former separation in embryonic
life into a pair of appendages. The labial palpi are three-jointed, the
joints being broad, and in life directed backwards instead of forwards
as in the higher insects.
There are five American species of the genus Lepisma in the Museum of
the Peabody Academy. Besides the common L. saccharina? there are four
undescribed species; one found about out-houses and cellars, and the
heat-loving form, perhaps an imported, species, found in a kitchen in
Salem, and apparently allied to the L. thermophila Lucas, of houses in
Brest, France; and lastly two allied forms, one from Key West, and
another from Polvon, Western Nicaragua, collected by Mr. McNiel. The
last three species are beautifully ornamented with finely spinulated
hairs arranged in tufts on the head; while the sides of the body, and
edges of the basal joints of the legs are fringed with them.
The interesting genus Nicoletia stands at the bottom of the group. It
has the long, linear, scaleless body of Campodea, in the family below,
but the head and its appendages are like Lepisma, the maxillary palpi
being five-jointed, and the labial palpi four-jointed. The eyes are
simple, arranged in a row of seven on each side of the head. The abdomen
ends in three long and many jointed stylets, and there are the usual
"false branchial feet" along each side of the abdomen. There are two
European species which occur in greenhouses. No species have yet been
found in America.
[Illustration: 153. Japyx solifugus.]
The next family of Thysanura is the Campodeæ, comprising the two genera
Campodea and Japyx. These insects are much smaller than the Lepismidæ,
and in some respects are intermediate between that family and the
Poduridæ (including the Smynthuridæ).
In this family the body is long and slender, and the segments much alike
in size. There is a pair of spiracles on each thoracic ring. The
mandibles are long and slender, ending in three or four teeth, and with
the other appendages of the mouth are concealed within the head, "only
the tips of the palpi (and of the maxillæ when these are opened)
projecting a very little beyond the rounded entire margin of the
epistoma," according to Haliday. The maxillæ are comb-shaped, due to the
four slender, minutely ciliated spines placed within the outer tooth.
The labium in Japyx is four-lobed and bears a small two-jointed palpus.
The legs are five-jointed, the tarsi consisting of a single joint,
ending in two large claws. The abdomen consists of ten segments, and in
Campodea along each side is a series of minute, two-jointed appendages
such as have been described in Machilis. These are wanting in Japyx.
None of the species in this family have the body covered with scales.
They are white, with a yellowish tinge.
The more complicated genus of the two is Japyx (Fig. 153, Japyx
solifugus, found under stones in Southern Europe; _a_, the mouth from
beneath, with the maxillæ open; _b_, maxilla; _d_, mandible; _c_,
outline of front of head seen from beneath, with the labial palpi in
position) which, as remarked by the late Mr. Haliday (who has published
an elaborate essay on this genus in the Linnæan Transactions, vol. 24,
1864), resembles Forficula in the large forceps attached to its tail. An
American species (J. Saussurii) lives in Mexico, and we look for its
discovery in Texas.
[Illustration: 154. Campodea staphylinus.]
Campodea (C. staphylinus Westw., Fig. 154, enlarged; _a_, mandible; _b_,
maxilla), otherwise closely related, has more rudimentary mouth-parts,
and the abdomen ends in two many jointed appendages.
[Illustration: Fig. 155. Larva of Perla.]
Our common American species of Campodea (C. Americana) lives under
stones in damp places. It is yellowish, about a sixth of an inch in
length, is very agile in its movements, and would easily be mistaken for
a very young Lithobius. A larger species and differing in having longer
antennæ, has been found by Mr. C. Cooke in Mammoth Cave, and has been
described in the "American Naturalist" under the name of Campodea
Cookei. Haliday has remarked that this family bears much resemblance to
the Neuropterous larva of Perla (Fig. 155), as previously remarked by
Gervais; and the many points of resemblance of this family and the
Lepismidæ to the larval forms of some Neuroptera that are active in the
pupa state (the Pseudoneuroptera of Erichson and other authors) are very
striking. Campodea resembles the earliest larval form of Chloëon, as
figured by Sir John Lubbock, even to the single jointed tarsus; and why
these two Thysanurous families should be removed from the Neuroptera we
are unable, at present, to understand, as to our mind they scarcely
diverge from the Neuropterous type more than the Mallophaga, or biting
lice, from the type of Hemiptera.
Haliday, remarking on the opinion of Linnæus and Schrank, who referred
Campodea to the old genus Podura, says with much truth, "it may be
perhaps no unfair inference to draw, that the insect in question is in
some measure intermediate between both," _i. e._, Podura and Lepisma.
This is seen especially in the mouth-parts which are withdrawn into the
head, and become very rudimentary, affording a gradual passage into the
mouth-parts of the Poduridæ, which we now describe.
The next group, the Podurelles of Nicolet, and Collembola of Lubbock,
are considered by the latter, who has studied them with far more care
than any one else, as "less closely allied" to the Lepismidæ "than has
hitherto been supposed." He says "the presence of tracheæ, the structure
of the mouth and the abdominal appendage; all indicate a wide
distinction between the Lepismidæ and the Poduridæ. We must, indeed, in
my opinion, separate them entirely from one another; and I would
venture to propose for the group comprised in the old genus Podura, the
term Collembola, as indicating the existence of a projection, or
mammilla, enabling the creature to attach or glue itself to the body on
which it stands." Then without expressing his views as to the position
and affinities of the Lepismidæ, he remarks "as the upshot of all this,
then, while the Collembola are clearly more nearly allied to the Insecta
than to the Crustacea or Arachnida, we cannot, I think, regard them as
Orthoptera or Neuroptera, or even as true insects. That is to say, the
Coleoptera, Orthoptera, Neuroptera, Lepidoptera, etc., are in my
opinion, more nearly allied to one another than they are to the Poduridæ
or Smynthuridæ. On the other hand, we certainly cannot regard the
Collembola as a group equivalent in value to the Insecta. If, then, we
attempt to map out the Articulata, we must, I think, regard the
Crustacea and Insecta as continents, the Myriopoda and Collembola as
islands--of less importance, but still detached. Or, if we represent the
divisions of the Articulata like the branching of a tree, we must
picture the Collembola as a separate branch, though a small one, and
much more closely connected with the Insecta than with the Crustacea or
the Arachnida." Lamarck regarded them as more nearly allied to the
Crustacea than Insecta. Gervais, also, in the "Histoire Naturelle des
Insectes: Aptères," indicates a considerable diversity existing between
the Lepismidæ and Poduridæ, though they are placed next to each other.
Somewhat similar views have been expressed by so high an authority as
Professor Dana, who, in the "American Journal of Science" (vol. 37,
Jan., 1864), proposed a classification of insects based on the principle
of cephalization, and divided the Hexapodous insects into three groups:
the first (Ptero-prosthenics, or Ctenopters) comprising the Hymenoptera,
Diptera, Aphaniptera (fleas), Lepidoptera, Homoptera, Trichoptera and
Neuroptera; the second group (Ptero-metasthenics, or Elytropters)
comprising the Coleoptera, Hemiptera and Orthoptera; while the Thysanura
compose the third group. Lubbock has given us a convenient historical
view of the opinions of different authors regarding the classification
of these insects, which we find useful. Nicolet, the naturalist who,
previous to Lubbock, has given us the most correct and complete account
of the Thysanura, regarded them as an order, equivalent to the
Coleoptera or Diptera, for example. In this he followed Latreille, who
established the order in 1796. The Abbé Bourlet adopted the same view.
On the other hand Burmeister placed the Thysanura as a separate tribe
between the Mallophaga (Bird Lice) and Orthoptera, and Gerstaecker
placed them among the Orthoptera. Fabricius and Blainville put them with
the Neuroptera, and the writer, in his "Guide to the Study of Insects,"
and previously in 1863, ignorant of the views of the two last named
authors, considered the Thysanura as degraded Neuroptera, and noticed
their resemblance to the larvæ of Perla, Ephemera, and other Neuroptera,
such as Rhaphidia and Panorpa, regarding them as standing "in the same
relation to the rest of the Neuroptera [in the Linnæan sense], as the
flea does to the rest of the Diptera, or the lice and Thrips to the
higher Hemiptera."
After having studied the Thysanura enough to recognize the great
difficulty of deciding as to their affinities and rank, the writer does
not feel prepared to go so far as Dana and Lubbock, for reasons that
will be suggested in the following brief account of the more general
points in their structure, reserving for another occasion a final
expression of his views as to their classification.
The Poduridæ, so well known by name, as affording the scales used by
microscopists as test objects, are common under stones and wet chips, or
in damp places, cellars, mushrooms and about manure heaps. They need
moisture, and consequently shade. They abound most in spring and autumn,
laying their eggs at both seasons, though most commonly in the spring.
During a mild December, they may be found in abundance under sticks and
stones, even in situations so far north as Salem, Mass.
[Illustration: 156. Smynthurus.]
The body of the Poduras is rather short and thick, most so in Smynthurus
(Fig. 156), and becoming long and slender in Tomocerus 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 Lipura and Anura, the lowest forms of
the group, the segments are all much alike in size.
The head is in form much like that of certain larvæ of Neuroptera and of
Forficula, an Orthopterous insect. The basal half of the head is marked
off from the eye-bearing piece (epicranium) by a V-shaped suture[10]
(Fig. 157, head of Degeeria; compare also the head of the larva of
Forficula, Fig. 158, in which the suture is the same), and the insertion
of the antennæ 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 distinctly separated by suture from the
surrounding parts of the head, thus affording one of the best
distinctive characters of the Poduridæ. 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 Poduridæ (see Fig. 176, _e_, eye of Anurida). The
antennæ are usually four-jointed, and vary in length in the different
genera.
[Illustration: 157. Head of Degeeria.]
[Illustration: 158. Larva of Forficula.]
The mouth-parts are very difficult to make out, but by soaking the
insect in potash for twenty-four hours, thus rendering the body
transparent, they can be satisfactorily observed. They are constructed
on the same general type as the mouth-parts of the Neuroptera,
Orthoptera and Coleoptera, and except in being degraded, and with
certain parts obsolete, they do not essentially differ.[11] On observing
the living Podura, the mouth seems a simple ring, with a minute labrum
and groups of hairs and spinules, which the observer, partly by
guess-work, can identify as jaws and maxillæ, and labium. But in
studying the parts rendered transparent, we can identify the different
appendages. Figure 159 shows the common Tomocerus plumbeus greatly
enlarged (Fig. 160, seen from above), 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 separated by a
deep suture from the clypeus, and is trapezoidal in form. The mandibles
and maxillæ are long and slender, and buried in the head, with the tips
capable of being extended out from the ring surrounding the mouth for a
very short distance. The mandibles (_md_, Fig. 159) are like those of
the Neuroptera, Orthoptera and Coleoptera in their general form, the tip
ending in from three to six teeth (three on one mandible and six on the
other), while below, is a rough, denticulated molar surface, where the
food seized by the terminal teeth is triturated and prepared to be
swallowed. Just behind the mandibles are the maxillæ, which are
trilobate at the end, as in the three orders of insects above named. The
outer lobe, or palpus, is a minute membranous tubercle ending in a hair
(Fig. 161, _mp_), while the middle lobe, or galea, is nearly obsolete,
though I think I have seen it in Smynthurus, where it forms a lobe on
the outside of the lacinia. The lacinia, or inner lobe (Fig. 161, _lc_;
162, the same enlarged), in Tomocerus consists of two bundles of
spinules, one broad like a ruffle, and the other slender, pencil-like,
ending in an inner row of spines, like the spinules on the lacinia of
the Japyx and Campodea and, more remotely, the laciniæ of the three
sub-orders of insects above referred to. There is also a horny,
prominent, three-toothed portion (Fig. 161, _g_). These homologies have
never been made before, so far as the writer is aware, but they seem
natural, and suggested by a careful examination and comparison with the
above-mentioned mandibulate insects.
[Illustration: 159. 161. 160. 162.
Tomocerus plumbeus and mouth-parts, greatly enlarged.]
The spring consists of a pair of three-jointed appendages, with the
basal joints soldered together early in embryonic life, while the other
two joints are free, forming a fork. It is longest in Smynthurus and
Degeeria, and shortest in Achorutes (Fig. 172, _b_), where it forms a
simple, forked tubercle; and is obsolete in Lipura and Anura, its place
being indicated by an oval scar. The third joint varies in form, being
hairy, serrate and knife-like in form, as in Tomocerus (Fig. 159, _a_),
or minute, with a supplementary tooth, as in Achorutes (Fig. 172,
_c_). This spring is in part homologous with the ovipositor of the
higher insects, which originally consists of three pairs of tubercles,
each pair arising apparently from the seventh, eighth, and ninth (the
latter the penultimate) segments of the abdomen in the Hymenoptera. The
spring of the Podura seems to be the homologue of the third pair of
these tubercles, and is inserted on the penultimate segment. This
comparison I have been able to make from a study of the embryology of
Isotoma.
[Illustration: 163. Catch holding spring of Achorutes.]
Another organ, and one which, so far as I am aware, has been overlooked
by previous observers, I am disposed to consider as possibly an
ovipositor. In the genus Achorutes, it may be found in the segment just
before the spring-bearing segment, and situated on the median line of
the body. It consists (Fig. 163) of two squarish valves, from between
which projects a pair of minute tubercles, or blades, with four rounded
teeth on the under side. This pair of infinitesimal saws reminds 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 shallow place in which to
deposit an egg. It is homologous in situation with the middle pair of
blades which composes the ovipositor 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. (This
is a catch for holding the spring in place.)
But all the Poduras differ from other insects in possessing a remarkable
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 Smynthurus, 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 together, on
the under side of stones, chips or, as in the case of Isotoma Walkerii,
under the bark of trees. They are round, transparent. The development of
the embryo of Isotoma in general accords with that of the Phryganeidæ
and suggests on embryological grounds the near relationship of the
Thysanura to the Neuroptera.
[Illustration: 164. 165. 166. 167.
Development of a Poduran.]
The earliest stage observed was at the time of the appearance of the
primitive band (Fig. 164, _a_, _b_, folding of the primitive band; _c_,
the dotted line crosses the primitive band, and terminates in a large
yolk granule) which surrounds the egg as in the Caddis flies. Soon
after, the primitive segments appear (Fig. 165; 1, antennæ; 2,
mandibles; 3, maxillæ; the labium was not seen; 5-7, legs; _c_, yolk
surrounded by the primitive band) and seem to originate just as in the
Caddis flies. Figure 166 is a front view of the embryo shortly before
it is hatched; figure 167, side view of the same, the figures as in Fig.
165; _sp_, spring; _l_, labrum. The labrum or upper lip, and the clypeus
are large and as distinct as in the embryos of other insects, a fact to
which we shall allude again. The large three-jointed spring is now well
developed, and the inference is drawn that it represents a pair of true
abdominal legs. The embryo when about to hatch throws off the egg-shell
and amnion in a few seconds. The larva is perfectly white and is very
active in its movements, running over the damp, inner surface of the
bark. It is a little over a hundredth of an inch in length, and differs
from the adult in being shorter and thicker, with the spring very short
and stout. In fact the larva assumes the form of the lower genera of the
family, such as Achorutes and Lipura, the adult more closely resembling
Degeeria. The larva after its first moult retains its early clumsy form,
and is still white. After a second moult it becomes purplish, and much
more slender, as in the adult. The eggs are laid and the young hatched
apparently within a period of from six to ten days.
Returning to the stage indicated by figures 166 and 167, I am induced to
quote some remarks published in the Memoirs of the Peabody Academy of
Science, No. 2, p. 18, which seem to support the view that these insects
are offshoots from the Neuroptera.
"The front of the head is so entirely different from what it is in the
adult, that certain points demand our attention. It is evident that at
this period the development of the insect has gone on in all important
particulars much as in other insects, especially the Neuropterous
Mystacides as described by Zaddach. The head is longer vertically than
horizontally, the frontal, or clypeal region is broad, and greater in
extent than the epicranio-occipital region. The antennæ are inserted
high up on the head, next the ocelli, falling down over the clypeal
region. The clypeus, however, is merged with the epicranium, and the
usual suture between them does not appear distinctly in after life,
though its place is seen in figure 167 to be indicated by a slight
indentation. The labrum is distinctly defined by a well marked suture,
and forms a squarish, knob-like protuberance, and in size is quite large
compared to the clypeus. From this time begins the process of
degradation, when the insect assumes its Thysanurous characters, which
consist in an approach to the form of the Myriopodous head, the front,
or clypeal region being reduced to a minimum, and the antennæ and eyes
brought in closer proximity to the mouth than in any other insects."
Sir John Lubbock has given us an admirable account of the internal
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 system of tracheæ in
Smynthurus which opens by "two spiracles in the head, opposite the
insertion of the antennæ," _i. e._, on the back of the head. (Von Olfers
says that they open on the prothorax.) Nicolet and Olfers claim to have
found tracheæ in several lower genera (Orchesella, Tomocerus, and
Achorutes and allied genera), but Lubbock was unable to detect them, and
I may add that I have not yet been able after careful search to find
them either in living specimens, or those rendered transparent by
potash.
Having given a hasty sketch of the external aspect of the Poduras, I
extract from Lubbock's work a synopsis of the families and genera for
the convenience of the student, adding the names of known American
species, or indications of undescribed native forms.
SMYNTHURIDÆ.--Body globular or ovoid; thorax and abdomen forming one
mass; head vertical or inclined; antennæ of four or eight segments. Eyes
eight on each side, on the top of the head. Legs long and slender.
Saltatory appendage with a supplementary segment.
Smynthurus. Antennæ four-jointed, bent at the insertion of the fourth,
which is nearly as long as the other three, and appears to consist of
many small segments. No conspicuous dorsal tubercles. (In this country
Fitch has described five species: S. arvalis, elegans, hortensis,
Novæboracensis, and signifer. Figure 156 represents a species found in
Maine.)
Dicyrtoma. Antennæ eight-jointed, five before, three after the bend. Two
dorsal tubercles on the abdomen.
Papirius.[12] Antennæ four-jointed, without a well-marked elbow, and
with a short terminal segment offering the appearance of being
many-jointed.
PODURIDÆ.--This family comprises those species of the old genus Podura,
in which the mouth has mandibles [also maxillæ and a labium], and the
body is elongated, with a more or less developed saltatory appendage at
the posterior extremity.
Orchesella. Segments of the body unequal in size, more or less thickly
clothed with clubbed hairs. Antennæ long, six-jointed. Eyes six in
number on each side, arranged in the form of an S. (One or two beautiful
species live about Salem.)
[Illustration: 168. Degeeria.]
Degeeria. Segments of the body unequal in size, more or less thickly
clothed by clubbed hairs. Antennæ longer than the head and thorax,
filiform, four-jointed. Eyes eight in number on each side of the head.
(Two species, Degeeria decem-fasciata, Pl. 10, Figs. 2, 3, and D.
purpurascens, Figs. 4, 5, are figured in the "Guide to the Study of
Insects." Figure 168 represents a species found in Salem, Mass., closely
allied to the European D. nivalis. Five species are already known in New
England.)
Seira. Body covered with scales. Antennæ four-jointed; terminal segment
not ringed. Eyes on a dark patch. Thorax not projecting over the head.
Abdominal segments unequal.
Templetonia. Segments of the body subequal, clothed by clubbed hairs,
and provided with scales. Antennæ longer than the head and thorax,
five-jointed, with a small basal segment, and with the terminal portion
ringed.
Isotoma. Four anterior abdominal segments subequal, two posterior ones
small; body clothed with simple hairs and without scales. Antennæ
four-jointed, longer than the head; segments subequal. Eyes seven in
number on each side, arranged in the form of an S. (Three species are
found in Massachusetts, one of which (I. plumbea) is figured on Pl. 10,
Figs. 6, 7, of the "Guide to the Study of Insects," third edition.)
Tomocerus. Abdominal segments unequal, with simple hairs and scales.
Antennæ very long, four-jointed, the two terminal segments ringed. Eyes
seven in number on each side. (The European T. plumbea, Podura plumbea
of authors, is our species, and is common. Fig. 160, greatly enlarged,
copied from Templeton; Fig. 159, side view, see also Fig. 161, where the
mouth-parts are greatly enlarged, the lettering being the same, _md_,
mandibles; _mx_, maxillæ; _mp_, maxillary palpus; _lb_, labium; _lp_,
labial palpus; _lc_, lacinia; _g_, portion ending in three teeth; _l_,
lobe of labium; _sp_, ventral sucking disk; the dotted line's passing
through the body represent the course of the intestine; _b_, end of
tibia, showing the tarsus, with the claw, and two accessory spines; _a_,
third joint of the spring. Fig. 162, lacinia of maxilla greatly
enlarged. Fig. 169, different forms of scales, showing the great
variation in size and form, the narrow ones running into a linear form,
becoming hairs. The markings are also seen to vary, showing, their
unreliable character as test objects, unless a single scale is kept for
use.)
[Illustration: 169. Scales of Tomocerus.]
[Illustration: 170. Lepidocyrtus.]
[Illustration: 171. Scale of Lepidocyrtus.]
Lepidocyrtus. Abdominal segment unequal, with simple hairs and scales.
Antennæ long, four-jointed. Eyes eight in number on each side. (Fig.
170, L. albinos, an European species, from Hardwicke's "Science Gossip."
Fig. 171, a scale. Two species live in New England.)
Podura. Abdominal segments subequal. Hairs simple, no scales. Antennæ
four-jointed, shorter than the head. Eyes eight in number on each side.
Saltatory appendage of moderate length.
[Illustration: 172. Achorutes.]
Achorutes. Abdominal segments subequal. Antennæ short, four-jointed.
Eyes eight in number on each side. Saltatory appendage quite short.
Figure 172 represents a species of this genus very abundant under the
bark of trees, etc., in New England. It is of a blackish lead color;
_a_, end of tibia bearing a tenant hair, with the tarsal joint and large
claw; _b_, spring; _c_, the third joint of the spring, with the little
spine at the base; figure 163, the supposed ovipositor; _a_, the two
blades spread apart; _b_, side view. The mouth-parts in this genus are
much as in Tomocerus, the maxillæ ending in a lacinia and palpus.
[Illustration: 173. Lipura fimetaria.]
The three remaining genera, Lipura, Anurida and Anura, are placed in the
"family" Lipuridæ, which have no spring. Lubbock remarks that "this
family contains as yet only two[13] genera, Lipura (Burmeister), in
which the mouth is composed of the same parts as those in the preceding
genera, and Anura (Gervais), in which the mandibles and maxillæ
disappear." Our common white Lipura is the European L. fimetaria Linn.
(Fig. 173, copied from Lubbock). The site of the spring is indicated by
an oval scar.
[Illustration: 174. 176. 175.
Anurida maritima.]
Figure 174 represents Anurida maritima found under stones between tide
marks at Nantucket. It is regarded the same as the European species by
Lubbock, to whom I had sent specimens for comparison. This genus differs
in the form of the head from Lipura and also wants the terminal upcurved
spines, while the antennæ are much more pointed. The legs (Fig. 175) end
in a large, long, curved claw. On examining specimens soaked in potash,
I have found that the mouth-parts of this species (Fig. 176,) _md_,
mandibles; _mx_, maxillæ; _e_, eyes, and a singular accessory group of
small cells, are like those of Achorutes, as previously noticed by
Laboulbène. The mandibles, like those of other Poduras, end in from
three to six teeth, and have a broad, many-toothed molar surface below.
The maxillæ; end in a tridentate lacinia as usual, though the palpi and
galea I have not yet studied.
The genus Anura may be readily recognized by the mouth ending in an
acutely conical beak, with its end quite free from the head and hanging
down beneath it. The body is short and broad, much tuberculated, while
the antennæ are short and pointed, and the legs are much shorter than in
Lipura, not reaching more than a third of their length beyond the body.
Our common form occurs under the bark of trees.
For the reason that I can find no valid characters for separating these
three genera as a family from the other Poduras, I am inclined to think
that they form, by the absence of the spring, only a subdivision
(perhaps a subfamily) of the Poduridæ.
The best way to collect Poduras is, on turning up the stick or stone on
the under side of which they live, to place a vial over them, allowing
them to leap into it; they may be incited to leap by pushing a needle
under the vial. They may also be collected by a bottle with a sponge
saturated with ether or chloroform. They may be kept alive for weeks by
keeping moist slips of blotting paper in the vial. In this way I have
kept specimens of Degeeria, Tomocerus and Orchesella, from the middle of
December till late in January. During this time they occasionally
moulted, and Tomocerus plumbeus, after shedding its skin, ate it within
a few hours. Poduras feed ordinarily on vegetable matter, such as dead
leaves and growing cryptogamic vegetation. These little creatures can be
easily preserved in a mixture of alcohol and glycerine, or pure alcohol,
though without the glycerine the colors fade.
We have entered more fully in this chapter into the details of structure
than heretofore, too much so, perhaps, for the patience of our readers.
But the study of the Poduras possesses the liveliest interest, since
these lowest of all the six-footed insects may have been among the
earliest land animals, and hence to them we may look with more or less
success for the primitive, ancestral forms of insect life.
FOOTNOTES:
[Footnote 9: Nicolet, in the "Annales de la Societe Entomologique de
France" (tome v, 1847), has given us the most comprehensive essay on the
group, though Latreille had previously published an important essay, "De
l'Organization Exterieure des Thysanoures" in the "Nouvelles Annales du
Museum d'Histoire Naturelle, Paris, 1832," which I have not seen.
Gervais has also given a useful account of them in the third volume of
"Apteres" of Roret's Suite a Buffion,
published in 1844.
The Abbe Bourlet, Templeton, Westwood, and Haliday have published
important papers on the Thysanura; and Meinert, a Danish naturalist, and
Olfers, a German anatomist, have published important papers on the
anatomy of the group. In this country Say and Fitch have described less
than a dozen species, and the writer has described two American species
of Campodea, C. Americana, our common form, and C. Cookei, discovered by
Mr. C. Cooke in Mammoth Cave, while Humbert has described in a French
scientific journal a species of Jupyx (J. Saussurii) from Mexico.]
[Footnote 10: The direct homology of these parts of the head (the
occiput and the epicranium) with Perla, Forficula, etc., seems to me the
best evidence we could have that the Poduræ are not an independent
group. In these most fundamental characters they differ widely from the
Myriopods. I am not aware that this important relation has been
appreciated by observers.]
[Footnote 11: As we descend to the soft, tube-like, suctorial (?) mouth
of Anura, which is said not to have hard mouth-parts, we see the final
point of degradation to which the mouth of the Thysanura is carried. I
think that this gradual degradation of the mouth-parts in this group
indicates that the appendages in these animals are not formed on an
independent type, intermediate, so to speak, between the mandibulate and
haustellate types, but are simply a modification (through disuse) of the
mandibulate type as seen in Neuropterous insects.]
[Footnote 12: Lubbock considers that Papirius should be placed in a
distinct family from Smynthurus, because it wants tracheæ. Their
presence or absence scarcely seems to us to be a family character, as
they are wanting in the Poduridæ, and are not essential to the life of
these animals, while in other respects Papirius seems to differ but
slightly from Smynthurus.]
[Footnote 13: Dr. Laboulbène has recently, and we think with good
reason, separated Anura maritima from the genus Anura, under the name of
Anurida maritima.]