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Psyche 4:245-250, 1883.

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THE GEOLOGICAL HISTORY OF MYRIOPODS AND ARACHNIDS. BY SAMUEL HUBBARD SCUDDER, CAMBRIDGE, MASS. [Eighth annual address of the retiring president of the Cambridge Entomolpgical Club.] As the only subject of a general nature
to which I have given recent attention I venture to invite you to review with me
the geological history, first of myriopods and then of arachnids. Unusual atten-
tion has recently been paid to these ani- mals, on account of the discovery of
their remains in formations much ear-
lier than those from which they had for
a long time been known, and the rela-
tion of these discoveries to our previous knowledge will be best brought out by
such a review, and it will, to a certain extent, be timely.
Our knowledge of the morphology,
systematic position and extent of the
myriopoda has been greatly increased
within a recent period. The discovery
of the minute Paurofus by Lubbock,
and the study of this and allied forms by Kyder and others, have led to the estab- lishment of the $am-o$oda as a type of
living myriopods of equal taxonomic
value to the two groups of chiZo$oda
and dijlo$oda which had long been
looked upon as the only divisions of the group. Modern investigations into the
structure of the anomalous Peri-fiatus
have extended our ideas concerning the
types allied to the myriopoda ; while the strange forms revealed by recent re-
searches in the carboniferous and devon- ian faunas have compelled us to recog-
nize a wider range in its structure and
a multiplication of its primary groups.
The relations of ancient to modern forms of life prove far more important and in- teresting in the myriopoda than in either the arachnids or the hexapoda. That
these relations are equally puzzling will appear from a brief review of the struct- ure and development of the different
groups.
In the eilrly life of the fauropoda and
of the diplopoda we have what may be
fairly considered a true larval form, in which, for a brief period after leaving
the egg, the body, much shorter than in
after life, is provided with three pairs of legs borne upon the anterior segments
of the body. These segments are never
more fully provided with legs, though
most of the segments posterior to them,
both those which exist during this larval period and those which originate subse-
quently, bear two pairs. In the chilo-
poda, on the other hand, although the
appendages of the anterior segments de-
velop earlier than those behind them,
there is no true larval condition, or
perhaps one may say a larval condition
is permanent, in that the same anterior
legs become early and permanently
developed as organs subsidiary to man-
ducation, while the segments of the
hinder part of the body develop only a
single pair of legs.
The larval condition and resultant
more or less highly developed metamor-
phosis of the higher hexapoda have been
looked upon by many as a secondary
after-development, and one which there-
fore in no sense gives any clue to the
historical development of the group,




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such as we frequently find mirrored in
the embryonic growth of other animals.
This view seems to be supported by a
comparison, of the modern ancl ancient
types of myriopoda. The larval charac-
teristics of the young of living types of myriopoda, marvelously analogous in
their main features to those of the larvae ofeven the higher hexapoda, are confined to the apodal nature of the abbreviated
abdomen, and more particularly to the
specialized development of appendages
on the segments directly following the
head. This specialized condition of the
anterior segments is, in a sense, analo- gous to the structure of the thorax of the l~exapod'ci and is persistent throughout life,-in the chilopoda in a marked
manner, in the other groups by the
isolation of these segments as bearing
but a single pair of legs. Now nothing
of this specialization appears in the
pdeozoic types, of which of course we
know only the mature forms ; but the
segments following the head differ in no point whatever from those of the re-
mainder of the body in the character
;uicl number of their appendages. In
one type, the archi$olyjoda, corres-
ponding in a measure to the living type
of diplo$& two pairs of leg's are borne
on every segment; while in the other,
the protosyq-7za.tJza^ corresponding in
a similar way to the chilopoda. a single pair of legs is found. If then we look
upon the specialization of the segments
(or the appendages of the segments)
immediately following the head in living myriopodan types as a secondary devel-
opment, or, we may say, as the initiatory stage in an acquiring metamorphosis ;
then we may perhaps consider the archi-
$o7ypoda as the true prototypes of the
di'lo-poda and possibly also of the
fiauropoda, and the frotosyngna/ha as
the prototypes of the chilopoda.
In this view, one principal distinction
between the modem di'opoda and
cJzilo$oda is shown to have existed
from paleozoic times, viz : that in one
group there are, over most of the body,
to each dorsal scute two ventral scutes, eat11 bearing a pair of legs ; in the
other group a single ventral scute with
a single pair of legs ; and it becomes
interesting to inquire whether we can
discover any indication of the condition of things from which this diversity of
structures arose, and what was the line
of development through which it passed.
It will also help to determine the ques- tion, whether the dorsal or the ventral
scutes of the dip/ojoda are to be looked upon as the homologs of those of the chi- lojodq or, in other words, whether the
dorsal scutes of the diplo$oda are coin- pound, or the ventral scutes of the same are to be looked upon as s~~bsegments.
It should be remarked at the outset
that what we know of the embryology
of recent types shows that in the dipio- poda two pairs of legs, in the chilo$oda one pair, arise from each original body
somite beyond the front portion of the
body. This would indicate that the
dorsal scutes of the two groups were
homologous ancl the ventral scutes of
the diplopoda should be looked upon
as representing subsegn~ents~ This,
however, is not the answer indicated
by the paleontological evidence, nor is
it what we shoulcl expect from, among




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other things, the presence of stigmata
This- indicates that the present dorsal
on each of the ventral scutes in diflo-
pod0 All the carboniferous archipoly-
pods show a clear indication of the
compound nature of the segments. Not
only were the ventral scutes far more
important and extensive than in the
modern di'Zo$o& but some at least
of the genera bore in addition to large
stigmata outside the legs, a pair of seg- mental organs next the inedioventral
line on each ventral scute; the dorsal
scute was also distinctly divided into two areas, an anterior and a posterior. In
some types this latter distinction was
more marked than in others, in some
being carried so far that under certain
conditions of preservation one would
readily take them to be entirely sepa-
rate; and this indeed appears to be
f
absolutely the case in the older clevo-
nian forms, from the lower old red sancl- stone of Scotland. These show an
apparently complete demarcation of the
dorsal scutes of each segment as well as of the ventral, and present therefore a
series of alternating larger and smaller segments, the larger bearing all the
dorsal cuticular outgrowths, but each
bearing a single pair of legs. Of this
primal condition of the body segments
the embryology of modern types gives
no hint, its earliest indications showing nothing anterior to what must have
been the condition of things wholly
posterior to the paleozoic epoch, at least so far as the cliplopodan series is con- cerned ; nothing anterior, indeed, to the fixed condition of the present type.
They are only borne in general on alternate seg- ments in chilopoda.
scutes of diplojoda are compound and
formed of two originally distinct scutes ; and that, as a later development of a
similar sort, the ventral scutes of the
anterior segments have likewise con-
solidated and lost each one pair of
appendages.
Under this view the line which we
follow back from the chilo-poda through
the frotosyng'natha is the more nearly
allied to the simple stock type. Yet it
is the other line which has been found
earliest in the rocks, clearly showing
that the actual origin of the myriopodan phylum must be looked for at the very
first appearance of land animals ; in-
deed the evidence that some of the
carboniferous types were amphibious
may warrant our belief that the type
may have fairly originated among aqua-
tic animals.
Fossil myi-iopoda were first made
known from the carboniferous rocks,
when Westvvood figured, in Brodie's
work on the older fossil insects of
England, the remains of what he sup-
posed to be a lepidopterous larva.
There had been indeed earlier refer-
ences by name merely to tertiary myri-
opoda from amber and from Aix (Ser-
res) , but it was not until the publications, thirty years ago, of Koch, Berendt and
Menge, that the amber species were
known, and to them hardly any ad-
ditions have since been made. In
1859 Sir William Dawson published the
first account of a paleozoic rnyriopod re- cognized as such, and since 1868 our
horizon, as regards the older forms, has been widened materially by the publica-
tions of Messrs. Dohrn, Meek and




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Worthen, Peach, Scudder, and Wood-
ward, until to-day the number of forms
known from pretertiary deposits is nearly as great as those from the tertiary.
The oldest known are those described
by Page and Peach from the lower old
red sandstone of Scotland -two species
belonging to the archifoZyfoda. In
the carboniferous formation the a d -
$oZy$oda culminate, showing a consid-
erable variety of generic types distinct from those of the devonian, and embrac-
ing nearly thirty species, of which by
far the greater number come from Amer-
ica, and the few remaining ones from
Great Britain, with
possibly a single
species from Germany. Four species,
imperfectly known, which have been
referred to /uZus, and which come from
the permian of central Europe may be-
long to the archiiolyfoda. The only
mesozoic forms known are the JuZ~$sis
cretacea of Heer, from Greenland,
which is either an archipolypod or a
cliplopod (it is impossible to tell which), and the uncertain Geoehs $roavus
of Munster from Solenhofen, which is
probably to be looked upon as a nereid
worm.
The tertiary species are still known
almost entirely from the work of Koch
and Berendt, and belong entirely to the
di-plopoda and chilo$o& the larger pro-
portion to the former. A few species,
however, have been indicated from Aix,
a single one described from the brown
coal of Rott and one from the Green
River deposits of North America. .
The following table presents a view
of the distribution of the myriopoda in
time.
The figures represent the
number of species.
Protosyngnatha ............
Chilopoda ..................
Archipolypoda.. ..........-.
Diplopoda ..................
Pauropoda .................
Paleozoic. 1 Mesozoic.
å 03
3
.a 0
0 (U
03 U
E $
2 E
u
- --
.......
(I?)
-..
.......
.
(I?,
.......
Cenozoic.
The geological history of arachnida,
which the order is divisible are repre-
as known at the present time, pre- sented in the older rocks, and these, sents some points of interest.
Only
which are not confined to the lower
a portion of the great groups into types, attain a degree of perfection and



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a diversity of structure inconsistent with a belief in our having reached the prim- ordial forms of this phylum in our
retrograde search.
When, in 1858, Bronn published his
prize essay on the distribution of fossils, only two species of pretertiary arach-
nida were known as such. one from the
carboniferous and one from the juras-
sic formation, and the knowledge of
tertiary forms was confined entirely to
the then recently published work of
Koch and Berendt on the species from
amber. Since then Menge has in-
creased somewhat our knowledge of the
amber fauna, and it includes to-day nine- tenths or more of the known tertiary
species. But it is only within the last
fifteen years that our knowledge of pre- tertiary anichnida has been extended
beyond the description of two or three
species. The number is still exceedingly few -between 20 and 30 species -but
it is being constantly extended, and the abundance of arthropods brought to
light in recent years in the carboniferous deposits of Allies, Bohemia, Scotland
and Illinois leads us to expect an early and considerable extension of the list.
This expectation is strengthened by
LindstGin's and Hunter's discoveries of
scorpions in the upper Silurian rocks of Gotland and Scotland.
The forms that have been found fossil
in the earlier formations have proved,
as might be expected, to belong mostly
to those having a dense integument,
and in the two species believed to be
true araneae, the abdomen was proba-
bly provided with more or less densely
chitinous dorsal plates. With these
two exceptions, and a single genus of
$edi$aI'i, all the paleozoic arachnida
(only a single mesozoic form is
known) belong either to the scoQio-
nides or to a peculiar group, the a h a - comwii.
This group is not found later,
and the single known species of me-
sozoic arachnida* is a true Amea. The
paucity of remains of arachnida in
mesozoic strata is somewhat remark-
able. Besides the species mentioned
above, only one other has been indicated, a species supposed to belong to the
ameae, from the English lias.
Thanks to the amber deposits of Prus-
sia, we know far more about the tertiary .
history of arachnida than would be
possible if our sole reliance were on the rocks, the latter furnishing us with only about double the number of those occur-
ring in pretertiary deposits. In the
amber alone occur all the suborders of
arachnida, excepting the fedifal-pi
and the already extinct adhacornart<
as well as all the families of araneae
excepting one peculiar to the jurassic ; but in the tertiary rocks neither chelone- + sco~$iones nor opilio~es have been
recognized ; of the fedi$aZ$& a single
species is referred to by Serres from the marnes of Aix, but too obscurely to
take account of it.
Examining the araneae alone, which
are far better represented in the tertiaries than are the other suborders, we find a
very large number of extinct genera.
In all, seventy-one are now known,
* Palpipes or Phalangites, believed even by Thorell to be an arachnid, has been shown by Seebach to be a stomatopodous crustacean.




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ate regions of Europe and North Amer-
ica that any arachnida have been found
in a fossil state, and these, so far as the indications have any meaning, invari-
ably point, whether in carboniferous or
tertiary deposits, to a warmer climate
than now obtains in the localities where they occur. This becomes more marked
when we reach the tertiary rocks and
can compare the types more closely
with existing forms, a n~~mber of the
genera, to which, for instance, the amber spiders belong, being now exclusively
tropical.
The following table gives a general
systematic view of the distribution of
arachnida in the different geological
formations since their first appearance
in the upper silurian.
sixty-six from Europe and thirteen from
America, eight being common to both.
Of these 37 are accounted extinct, 35
from Europe and 2 from America, and
none of these have been found on both
continents.
In the stratified tertiary deposits the
same families of araneae are in every
instance found in Europe and America,
excepting the dysderides, which family
has a single representative in America
and none in Europe.
It also appears
that just those families which are repre- sented abundantly in amber are also
found to some extent in the American
tertiary fauna, and (excepting-, as be-
fore, the dysderides) in the European
rocks.
It is only in the rocks of the temper-
Cenozoic.
Paleozoic.
Mesozoic.
The figures represent the
number of species.
Acari .................
............ Chelonethi
Anthracomarti .........
.............. Pedipalpi
Scorpiones ............
Opiliones ..............
Araneae
......... Saltigradae
........... Citigradae
Laterigradae .......
Territelariae ........
.........
Tubitelariae
Retitelariae .........
Orbitelariae ..-......




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