grows thicker from the base to the apex, as in the majority of
_Coleoptera_, _Hymenoptera_, &c.; in the _Orthoptera_, _Neuroptera_,
&c., it is generally equally thick every where. Another peculiarity
relating to this head observable in it, is its tendency to a trigonal
figure: this, however, though very general, is not universal;--thus,
in some _Orthoptera_, as _Pterophylla_ K., its horizontal section is
quadrangular; in others, as _Locusta_ Leach and many other insects,
it is nearly a circle; in some scorpions it is almost a hexagon. The
superficial shape also of this joint in numerous instances is more or
less triangular, but it sometimes recedes from this form:--thus, in
_Callichroma latipes_ it is a segment of a circle; in some _Empides_
it is clavate; in _Onitis Sphinx_, dolabriform; in the _Orthoptera_,
_Neuroptera_, &c., it is usually linear; in some _Lygæi_ it is
angular[2034]: but the most remarkable _tibiæ_ in this respect are
those of such species of this last genus as have the posterior
ones winged or foliaceous, so that they resemble the leaf of some
plant--the _tibia_ being the _rachis_, and the _wing_ (which in some
species is veined) representing the _leaf_ itself. This structure
is exemplified in _Lygæus compressipes_, _phyllopus_, _foliaceus_,
&c.[2035] Under this head I must say a few words upon the _flexure_
of this joint, which in some cases merits notice. I have before
mentioned its bend at the knee[2036] or base: the apex also is
sometimes incurved--in the anterior one of the male of _Macropus
longimanus_ so as almost to form a hook[2037]: in _Lygæus Pharaonis_
the posterior pair are flexuose[2038]; in _Bruchus Bactris_,
_Leucospis_, and several species of _Chalcis_, these _tibiæ_ curve
so as to adapt themselves to the bend of the thigh when folded. The
notch on the inside of the anterior pair, in a large majority of
_Carabus_ L., armed above by a spur[2039], a structure which probably
assists them in seizing and detaining their prey, may also here be
introduced: in the generality it is a little removed from the apex of
the joint in question; but in _Pamborus_ it is very near to it, and
in _Cychrus_, _Carabus_, &c., it becomes obsolete. I may mention here
also a singular character which distinguishes the cubit of both sexes
of _Gryllus campestris_, _domesticus_, &c. At the base there is an
aperture which passes through the joint--anteriorly it is oval, and
posteriorly elliptical and much larger, and on both sides is closed
by a tense membrane.
The most striking peculiarities as to the _clothing_ of his joint have
been chiefly noticed under the sexual characters of insects[2040],
but some appear not to be of that description. In _Sphæridium_ Leach,
while the thighs and _tarsi_ are naked, the posterior _tibiæ_ are
remarkably beset with stiff bristles; in _Empis pennipes_ they are
thickly fringed on both sides; in _Scarabæus_ M^cL. only externally,
and in _Dytiscus serricornis_ internally; in _Necydalis barpipes_ K.
this fringe is longer at the apex; and in _Saperda hirtipes_ Ol. the
same _tibiæ_ at that part are adorned with a large brush, like that
observable in the antennæ of some _Lamiæ_[2041].
I must next call your attention to the _teeth_, _spines_, and _spurs_
with which the _tibiæ_ of insects are sometimes armed. With regard
to _teeth_, you have doubtless often observed those that distinguish
the _cubitus_ of the arm of most Lamellicorn beetles: these vary
in number from _one_, as in _Trox suberosus_, to _seven_, as in
_Geotrupes autumnalis_; but the most universal number is _three_:
in some species of _Geotrupes_, as _G. stercorarius_, &c., the
_third_ tooth from the apex, and those that follow it, may be called
_double_. These teeth, in their cubit or anterior shank, doubtless
assist these insects in burrowing. The four posterior _tibiæ_ in
this tribe are also distinguished by a kind of teeth which occupy
their whole diameter, and resemble so many steps. I have before
noticed the remarkable cubit of the _Gryllotalpa_, and likewise that
of _Scarites_, _Pasimachus_, &c., in which some of the teeth are
prolonged into _spines_[2042], which are the next description of
tibial arms that I mentioned. Spines are of _two_ kinds--those which
are merely _processes_ of the crust of the _tibia_, and those that
are _implanted_ in it, and seem to have a _gomphosis_ or perhaps an
_amphiarthrosis_ articulation[2043]. An instance of the _first_ kind
may be seen in the hind-legs of some grasshoppers[2044] (_Locusta_
Leach), the _Rutelidæ_, &c. though in others they are implanted:--of
the _second_, in the _cubitus_ of the _Mantidæ_, and of _all_ the
_tibiæ_ of the dragon-flies (_Libellulina_ M^cL.)[2045];--and of
_both_ kinds in the hind-legs of _Acrida_ K., those which arm the
upper angles of the tibiæ being _processes_, and those of the lower
being _implanted_. The term _spine_ I think ought to be restricted
to the first kind; the _second_ ought rather to be denominated
_spurs_ (_calcaria_), and may perhaps be regarded as in some degree
synonymous with those most important appendages of the joint in
question, that are implanted in or near their apex, which have been
hitherto distinguished by this last denomination, and which I am
next to consider. But though I have not altered a term generally
adopted, I must here express my opinion that they ought rather to be
considered as minute _toes_ or _fingers_, and that the denomination
best agreeing with their functions, as accessories to the main toe,
would be _digituli_: this is proved particularly by a character
peculiar to those of many species of the genus _Cimbex_ amongst the
saw-flies, in which these organs are furnished with a _sucker_ or
_pulvillus_ (as they are also in _Œnas_ a kind of blister beetle),
as well as the joints of the tarsi[2046]; which makes it evident
that they are applied by the animal to surfaces, and assist it in
walking or climbing; and in general it may be observed that in most
insects their principal use is connected with these motions, and with
burrowing. This circumstance tends to prove that the generality of
insects (for all have not these organs) have really a didactyle or
tridactyle hand or foot; and the hypothesis so often alluded to--that
the _cubitus_ or _tibia_, &c., is really analogous to the _carpus_
or _tarsus_ in vertebrate animals[2047]--seems to receive no small
confirmation from it; since, if the _spurs_ be really analogous to
_fingers_ or _toes_, the part they articulate with cannot be the
_tibia_, &c. Though the parts in question did not escape the notice
of Reaumur, Linné, De Geer, Latreille, &c., yet they have not been
employed in the determination of tribes, genera, &c., except by the
author last named, but perhaps adopted from Bonelli[2048], in the
subgenera _Zabrus_ and _Pelorus_: in many instances, however, they
afford excellent subsidiary characters, sometimes common to a whole
Order, and at others distinguishing its various subdivisions. With
regard to their _number_--I have noticed many variations which I
will now state to you, first observing that I shall express them by
_three_ figures, the _first_ representing the number of spurs on the
_anterior_ leg, the _second_ that of those on the _intermediate_,
and the _third_ on the _posterior_; and where there are spurs, as in
the _Trichoptera_ and _Lepidoptera_, on the _middle_ as well as at
the _end_ of the _tibia_, I shall express it by one figure _over_
another, the upper one representing the number of the _middle_ spurs.
If you make an examination yourself, it will be proper to remind
you that these little organs are extremely liable to be broken off,
but the socket in which they were planted is usually very visible.
The most _natural_ number is represented by 2:2:2; this you will
find very prevalent in the _Coleoptera_ Order, as in the Predaceous
and numerous other beetles: in the _Orthoptera_ and _Hemiptera_
Orders, however, I have not discovered an instance of it; but in
all the rest it more or less occurs: next to this number--_tibiæ_
with obsolete or no spurs seem most prevalent, particularly in the
_Hemiptera_; not a single instance of an insect furnished with them
occurring to me in the _Heteropterous_ section; and it is doubtful
whether there are any in the _Homopterous_.--Having stated the most
universal structure in this respect, I will next consider the Orders
seriatim. Amongst the _Coleoptera_ though the numbers 2:2:2 are most
frequent in occurrence, yet there are numerous exceptions. Thus, in
the Lamellicorns, 1:1:1 represents the _calcaria_ of one tribe of
the _Scarabæidæ_ M^cL. formed of the genus _Scarabæus_ M^cL.; 1:2:1
represents those of another tribe of that family, including the
subgenera _Ateuchus_, _Copris_, _Phanæus_, &c.; 1:2:2 again forms
the character in this respect of _Aphodius_ and the great majority
of the Lamellicorns; while 2:2:2 is confined in this section to
_Æsalus_ F. and _Melolontha chrysomeloides_ Schranck (_Psephus_
M^cL. MS.). In the other tribes of _Coleoptera_ other numbers occur.
Thus, 0:1:1 characterizes _Hylœcetus_; 0:1:2 _Mordella_; 0:2:2
_Macropus_; 1/1:2:2 _Harpalus_, and all those _Carabi_ L., except
_Zabrus_, that have a _notch_ in their anterior _tibiæ_; 1/2:2:2
_Zabrus_. In the _Orthoptera_ Order it is not easy to distinguish
the real _spurs_ from the implanted _spines_ that frequently arm
the legs: these in _Blatta_ are extremely numerous, even at the
apex of the _tibiæ_; but I cannot distinguish any that can be
regarded as true analogues of the former: the most natural number
of spurs in this Order is represented by 0:0:4; this you will see
in all the Locusts; in _Acrida_, _Conocephala_, _Pterophylla_; and
in _Truxalis_, _Pneumora_, &c.; in _Phasma_ there are none. In
_Mantis_, if the terminal process of the _cubitus_ is excluded,
it will be 0:2:2; in _Gryllotalpa_, admitting the terminal teeth
of that part[2049] as analogues of spurs, the number is 4:4:4;
in _Tridactylus_ Latr. 0:0:5[2050]; in _Gryllus_ Latr. 3:3:5; in
_Gryllus monstrosus_, 4:4:6. In the whole _Hemiptera_ Order I have
discovered no instance of an insect furnished with the real spurs:
for though in _Tettigonia_ F., _Cercopis_, &c., there are implanted
spines in the posterior _tibia_, and several at the apex, there are
none of them clearly analogous to real spurs. In the _Lepidoptera_
the most general arrangement appears to be 1/0:2:2/2; and next to
this, 1/0:2:2. In this Order most commonly there is no spur at the
end of the cubit, but one resembling a thumb[2051] arms its middle;
in _Pieris_, &c., this thumb is not present, so that the number is
0:2:2; in _Agarista_ Leach, _Erebus_, &c., you will find 1/0:2:4,
the posterior _calcaria_ being all terminal; and in _Attacus Atlas_,
all these organs are obsolete except the thumb. In the _Neuroptera_
the most general arrangement is 2:2:2; but in the _Libellulina_,
although the legs are very spinose, there are no spurs. In the
_Trichoptera_ K., in _Phryganea rhombica_ and affinities, the number
of them is expressed by 1/2:1/2:1/2; and in those with long antennæ,
_P. atra_, &c., by 2/2:2/2:2/2. In the _Hymenoptera_ the number 1:2:2
is most prevalent; and next to this, as in _Apis_ L., 1:1:2. In the
_Ichneumones minuti_ L. the spurs are 1:1:1; in _Atta_ Latreille, a
kind of ant[2052], 1:0:0. In the _Diptera_ it is often difficult to
distinguish the spurs from the spines; but the number most universal
is, I think, 2:2:2; in _Tipula_ it is 1:2:2; in the _Tabanidæ_ 0:2:0;
and in _Culex_, _Limonia_, &c., there are none. Amongst the insects
with more than six legs, most commonly the tibiæ have no spurs; but
in the _Araneidæ_ each is armed with _two_, a circumstance which also
distinguishes the corresponding joint of the _pedipalpi_.
These little organs inosculate each in an appropriate socket of the
end, or in many cases of the middle of the _tibia_; and that part
of their head or base that is received by it, is often constricted
for the purpose: from hence it follows that they are capable of some
degree of motion, but in some insects, as those on the four posterior
legs of _Scarabæus sacer_ and its more immediate affinities, and
those at the end of the cubit of _Gryllotalpa_, they are immoveable,
and appear almost processes of the joint to which they belong. They
are commonly sharp, of a subtriquetrous figure, with the lower side
flat: where there are two, the outer one is usually the longest; and
in general the spurs on the hind legs are longer than those on the
four anterior: but there are exceptions--thus, in _Acanthopus_ Latr.
the _intermediate_ spurs are the longest; and in _Cicindela_ the
_anterior_ are longer than the former; in _Blaps mortisaga_ those
on all the legs are nearly equal in length. They vary sometimes in
_shape_--those on the middle of the cubit of many _Lepidoptera_,
which may be regarded as a kind of thumb[2053], are of a lanceolate
shape; in _Meloe_ the external posterior one is flat and obtuse;
in _Œnas_ Latr. it is obconical, concave at the extremity, and
apparently furnished with a sucker; in _Ateuchus smaragdulus_ the
_anterior_, and in _Copris Carolina_ the _posterior_ is forked and
emarginate; in _Sirex_ the former is hooked and winged; in _Lamprima_
it is triangular and dilated; in _Aphodius analis_ it is dolabriform;
in _Dynastes retusus_ and _Juvencus_ the spurs are bent like a bow.
In many _Hymenoptera_, as the _Sphecidæ_, they are pectinated[2054],
with a series of minute parallel spines--a structure which assists
the animal in burrowing[2055]; in _Acanthopus_ Latr. they are armed
with little teeth or spines[2056]; in the hive bee the spur of the
cubit is furnished with a membranous appendage which I have called
the velum[2057]; and in a subgenus related to _Saropoda_ Latr.
(_Ctenoplectra_ K. MS.), the interior spur of the posterior leg is
crescent-shaped, fixed transversely, and fitted on the inner side
with a membrane, the edge of which is finally pectinated.
e. _Tarsus_ or _Manus_[2058]. This is the _last_ portion of the leg,
usually supposed to be analogous to the hand or foot of vertebrate
animals; but, according to the hypothesis so often alluded to, rather
the representative of their jointed finger or toe. In treating of
this part I shall consider its _articulation_ with the _tibia_,
and of its joints _inter se_; the _number_ of those joints; their
_proportion_ and _shape_; their _parts_ and _appendages_.
I seem to have observed _three_ kinds of tarsal _articulation_. The
_first_ is a species of _enarthrosis_ or ball and socket, the joints
terminating in a globular head, perforated indeed for the transmission
of muscles, &c., and which is received by a corresponding cavity of the
_tibia_ or preceding joint, as may be seen in many weevils (_Curculio_
L.[2059]). This admits of some rotatory motion.--The _second_ is a
_mixed_ articulation between _enarthrosis_ and _ginglymus_, when at the
base of the ball a deep transverse channel receives a corresponding
ridge of the _tibiæ_ or preceding joint: this may be found in _Rutela_
and probably many other Lamellicorn beetles; and something very similar
in the Predaceous ones.--The _third_ kind is where there is little or
no inosculation, and the joints are scarcely more than _suspended_:
this takes place in the _Orthoptera_, _Neuroptera_, &c.; but in
_Blatta_ and the hind legs of _Mantis_ there is some approach to the
foregoing kinds.
We are now to consider the _number_ of joints of the _tarsus_, which
varies considerably in the different Orders, and in one has been
assumed as a clue for a subdivision of it into sections[2060], which,
though not perfectly natural, is very convenient, and has been adopted
by most modern Entomologists. In treating of this head, I shall use
those denominations that have been employed by M. Latreille and others
to express the variations of the number of the tarsal joints in the
_Coleoptera_, but shall apply them to insects in general. Insects in
this view, therefore, may be called _pentamerous_; _heteromerous_;
_tetramerous_; _trimerous_; _dimerous_; or _monomerous_.
_Pentamerous_ insects are those which have _five_ joints in _all_
their _tarsi_. This is the most universal, and may be called the
_natural_ number of these joints. More than half the _Coleoptera_
belong to this section; in the _Orthoptera_--the _Blattidæ_, _Mantidæ_,
and _Phasmidæ_; all the _Lepidoptera_ except those butterflies called
_tetrapi_ (_Vanessa_, &c.); all the _Trichoptera_, _Hymenoptera_,
and _Diptera_; in the _Neuroptera_--_Ascalaphus_, _Myrmeleon_,
_Hemerobius_, _Corydalis_, &c.; and in the _Aptera_--_Pulex_[2061].
_Heteromerous_ insects are those in which the number of these joints
varies in the different pairs of legs[2062]. These variations, like
the spurs, may be expressed by three figures, the first representing
the _anterior tarsus_, the second the _intermediate_, and the third
the _posterior_. I begin with 5:5:4. This number represents those
beetles that have been _exclusively_ regarded as _heteromerous_ by
modern Entomologists--of this description is the Linnean _Tenebrio_,
_Meloe_, &c., now subdivided into numerous genera; they have _five_
joints in the two anterior pair, and _four_ in the posterior. The
tarsal joints of the aquatic genus _Hydroporus_ (a singular anomaly
in the Order to which they belong) are expressed by 4:4:5, thus
reversing the number in the preceding tribe: other Heteromerous
genera are to be found amongst the _Hemiptera_. Thus, in _Ranatra_
the numbers are 2:1:1; in _Sigara_ and _Nauceris_ 1:2:2; in a new
subgenus between _Belostoma_ and _Naucoris_ (_Xiphostoma_ K. MS.),
brought by Dr. Bigsby from Canada, 3:2:2; in the _Lepidoptera_ the
butterflies called _tetrapi_ (_Vanessa_, &c.) may be expressed
by 1:5:5. Amongst the _Aptera_ and _Arachnida_ there are three
remarkable genera, which if their pedipalps are included may
be deemed Heteromerous. I mean _Phrynus_, _Thelyphena_, and
_Galeodes_;--in the former the numbers will be *:4:4:4, the asterisk
denoting more than ten; in the second, 8:4:4:4.; and in _Galeodes_
(in which the first pair of pedipalps are not chelate, the mandibles
performing their office) the numbers are 1:1:3:3:3.[2063]
_Tetramerous_ insects are those in which all the _tarsi_ consist of
_four_ joints; these in the _Coleoptera_ are next in number to the
_pentamerous_--indeed a very large proportion of them strictly speaking
are really of the latter description, since in Linné's four great
genera, _Curculio_, _Cerambyx_, _Chrysomela_, and _Cassida_ and some
others, the _claw-joint_ (_ungula_) consists of _two_ articulations,
one very short, forming merely the ball at its base[2064], which
inosculates in the socket of the preceding joint, and the other
constituting the remainder: if you carefully separate these two pieces,
you will find that the last inosculates in the summit of the ball, and
is moved by appropriate muscles[2065]. This structure probably permits
the readier elevation and depression of this joint. In the _Orthoptera_
the tetramerous genera are those which Linné called _Tettigonia_
amongst his _Grylli_ (_Locusta_ F.); _Acheta monstrosa_ also, and in
the _Neuroptera_, _Raphidia_ belong to this section.
_Trimerous_ insects are those whose _tarsi_ consist of only _three_
joints. Amongst beetles the Lady-birds (_Coccinella_ L.) are
remarkable for this structure, but in them the claw-joint is also
_biarticulate_, so that strictly speaking they are _tetramerous_;
in the _Orthopterous_ Order the migratory locusts (_Locusta_ Leach)
belong to this section, as likewise _Gryllus_ Latr. and _Gryllotalpa_
Latr.: in the first of these genera is an appearance of there being
more joints in the _tarsus_, because there is more than one cushion
below the first[2066]. To this section also belong the great majority
of the _Hemiptera_, excluding only those tribes that connect the two
sections of the Order constituting the two Linnean genera _Nepa_ and
_Notonecta_; the _Libellulina_ likewise belong here, as do also the
_Scorpionidæ_ and _Scolopendridæ_.
_Dimerous_ insects are those that have _two_ joints in all their
_tarsi_. Such are the _Pselaphidæ_ in the Coleoptera Order[2067];
in the _Hemiptera_--_Belostoma_ and _Notonecta_; in the hexapod
_Aptera_--_Pediculus_; in the octopod--the _Acari_ of Linné; in the
myriapod--_Iulus_; and in the _Arachnida_--the _Araneidæ_.
_Monomerous_ insects are those which have only a single tarsal
joint. Only one Coleopterous and also one Hemipterous genus is so
distinguished: the first is _Dermestes Armadillus_ De Geer[2068], and
the second the common water-scorpion, _Nepa_ Latr. Among the _Aptera_
we find _Nirmus_, _Podura_, _Sminthurus_, &c., that belong to this
section.
To the above sections another may be added for those insects whose
_tarsi_ have more than _five_ joints, which may be denominated
_Polymerous_. Here belong the genera _Gonyleptes_ K., _Phalangium_
and _Scutigera_ Latr. In the first the number of joints varies from
_six_ to _eleven_, and in the two last they far exceed that number,
amounting in some species of _Phalangium_ to more than _fifty_, and
becoming convolute like the antennæ of Ichneumons[2069].
I am next to notice the _proportions_ and _shape_ of the _tarsus_ and
its joints. The most general law is, that it shall be shorter and more
slender than the _tibia_; but it admits of several exceptions--thus,
in _Megasoma_ K.[2070], in _all_ the legs; in _Agrostiphila_ M^cL.
MS.[2071] in the _intermediate_, and in _Amphicoma lineata_ in the
_posterior_ pair the _tarsi_ are the longest; in _Trichius Delta_
these last are longer than the thigh and _tibia_ together. In some
insects the _tarsi_ are disproportionally short, as in _Cassida_,
the _Pselaphidæ_, _Locusta_ Leach, &c. Though generally more slender
than the _tibia_, in several instances they are as thick or thicker,
or more dilated, as in most of the tetramerous beetles, which being
climbers require a dilated _tarsus_. Again, comparing the three pairs
of this joint with each other, the most general rule is, that the
_anterior_ should be the _shortest_, and the _posterior_ the _longest_:
but in some, as the Capricorn beetles, &c., they are nearly equal in
length; in others, as _Lytta marginata_, the _anterior_ pair, and in
_Rhipiphorus_ the _intermediate_, are the longest; in _Trichius Delta_
these last are the shortest. With respect to _thickness_, the anterior
_tarsi_, except in many males[2072], are not very strikingly different
from the rest.
With regard to the proportion of the joints of the _tarsus_ to each
other,--according to the most general law, the first is the longest,
the last next in length, then the second and third, and the fourth is
the shortest. In _Gonyleptes_ K. and other _Phalangidæ_ the first is
almost thrice the length of all the rest taken together; but there
are numerous exceptions to the rule. In the female _Carabi_ the first
joint is not longer than the last, and in the males not so long; and
in _Hydrophilus_, &c., it is the shortest of all. Again, the second
joint is longer than the three following ones in _Dasytes ater_[2073];
and than the last in _Cicindela sylvatica_: the _third_ joint is
shorter than the fourth in _Lampyris ignita_: it is longer than the
first in _Donacia_, many _Melolonthidæ_, &c. Once more, the _fourth_
joint, usually the shortest of all, is longer than the second and
third in _Anthia_, &c. Lastly, the claw-joint, usually the second in
length, in the _Eproboscidea_ Latr. (_Hippobosca_ L.) is very long and
large, while the four first joints are so extremely short as to be
scarcely distinguishable from each other: it is the shortest of all in
_Colymbetes_, &c.; it is of the length of the _third_ in _Cicindela
sylvatica_, of the _fourth_ in _C. sexguttata_. Though commonly the
slenderest joint of all, particularly so in _Raphidia_, in many
Heteromerous and Lamellicorn beetles it is the largest, conspicuously
so in _Mellinus tricinctus_. Sometimes, as in _Buprestis chrysis_, &c.,
all the tarsal joints are nearly equal in length and thickness.