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Richard Lydekker.

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largely open, its bones taking the form of long bars.
In some lizards, as in the one of which the skeleton

LEFT SIDE OF THE VERTEBRA OF is %ured, the upper surface of the skull is covered
A SNAKE. by bone, so that the temporal fossa- are roofed

over.

Ribs and Another important feature of the order is to be found in the

vertebra. c'.iivimistanre thai the ribs in the region of the back are single-headed,

and are articulated to the backbone by means of a facet (d) situated on the body

of each vertebra. This feature at once distinguishes the order from the crocodiles

and dinosaurs, in which the ribs are two-headed, and in the buck articulate to a




LIZARDS.



107



long process arising from the arches of the vertebrae ; from the tortoises, where the
single-headed ribs articulate at the junction between the bodies of two vertebrae ;
and from the plesiosaurs, in which the single-headed ribs of the back are articulated
to processes or facets on the arches of the vertebras. In most of the members of
the order the body of each vertebra has a cup in front and a ball behind, by which
it articulates with the adjacent segments of the column an arrangement paralleled
amonp- modern crocodiles. In some lizards, and in all snakes, the vertebrae, as

o

shown in the figure on p. 6, have additional surfaces on their arches for mutual
articulation, thus communicating additional flexibility, and at the same time strength
to the backbone.

Another important feature in which the order differs from all

Other Characters .111 u j. c i i i

the preceding ones, is the absence or any system or true abdominal

ribs, or of their equivalent, a plastron, on the inferior surface of the body. As
regards the teeth, these differ from those of the orders hitherto considered in that,
instead of being implanted in separate sockets, they are firmly soldered to the bones
of the jaw. In some cases they are attached to the very summit of the jawbones, when
the dentition is said to be acrodont ; while in others they are affixed to one of the
side-walls of the free edges of the jaws, the term pleurodont being then employed.
Another divergence from both crocodiles and tortoises is to be found in the vent
opening by a transverse aperture, whereas in the former group it is longitudinal,
and in the latter either circular or longitudinal. Finally, in those forms in which
the bones of the chest attain their fullest development, there is a breast-bone or

irnum, a pair of collar-bones or clavicles, and a median T-shaped interclavicle.
Special ^ ne a bove being the leading characters of the entire order of

Characters of scaled reptiles, it remains to consider how the lizards (Lacertilia) are
Lizards. ^ Q ^ e distinguished from the other two suborders into which the

dsting members of the assemblage are divided. Externally, by far the greater

imber of lizards are four-limbed reptiles of a crocodile-like appearance, with the
lead, neck, body, and tail well distinguished from one another, and if we had these
alone to deal with, there would be no sort of difficulty in distinguishing between a
lizard and a snake. The matter is, however, somewhat complicated by the circum-
stance that certain lizards, like the familiar slow-worm, lose all external traces of
limbs, and assume an elongated snake-like form, with the head passing imperceptibly
into the body without the intervention of a distinct neck, and without any external
indication of where the body ends and the tail commences. Externally, such snake-
like lizards are very difficult to distinguish from snakes, but on opening the mouths
of the former it will be found that the tongue cannot be withdrawn into a sheath
at its base, as is always the case with the latter. Further help in discriminating
between the two is afforded by the circumstances that whereas snakes have neither
eyelids nor external ear-openings, both these are usually, although not invariably,
present in the limbless lizards. As additional distinctive features of the present
group, by means of which they can be distinguished both from snakes on the one
hand and from chameleons on the other, the following points may be noticed. In
all lizards the two branches of the lower jaw are united at the chin by means of a
bony suture ; while in all the species furnished with limbs collar-bones are present ;
and when the limbs are absent, some traces of the bones forming what is known



io8 LIZARDS.

as the shoulder-girdle persist. In form the tongue is flattened, and, as already
said, cannot be withdrawn into a basal sheath, although such a sheath may be
present. In most of the members of the suborder the upper surface of the body is
clothed with the overlapping scales characteristic of the order in general, these
scales being in some cases underlain by bony plates ; but in most geckos the upper
scales are granular, although sometimes juxtaposed.

Numbers and Numerically, lizards are by far the most abundant of all reptiles

Distribution. a fc {,} ie present day, the total number of species not falling far, if at
all, short of one thousand seven hundred, which are arranged under twenty distinct
families. In this abundance at the present day, coupled with the specialised
features of the greater part of their organisation, lizards may be regarded
as occupying a very similar position in the reptilian class to that held by the
perching birds in the preceding class. With the exception of the polar and sub-
polar zones, lizards are distributed over the whole globe, ranging in some districts
from the level of the sea to the limits of eternal snow, and found alike in fruitful




SKELETON OF LIZARD.



and barren districts, in the neighbourhood of water, and in the most arid deserts.
Whereas, however, in the colder regions they are poor in species and small in size,
it is in the tropics and subtropical regions that they attain their maximum
development, as regards numbers, bodily size, richness of coloration, and peculiarity
of form.

As regards their distribution over the surface of the globe, lizards present a
most remarkable difference from what obtains among Amphibians (frogs, newts,
etc.), and, to a less degree, among tortoises. For instance, whereas Amphibians,
and to some extent tortoises," Pli eir distributional areas defined equatorially,
such lines of division, in the case of the t "ent group, must be drawn nieridioimlly.
Thus, in the case of Amphibians, one great distributional province includes Europe.
Asia, and North America, and the second embraces the regions lying south of the
lv|iiutor; whereas in the case of lisa ^ne area marked by peculiar forms will
include the Old World and ^ oiher will comprise the whole of

America. As has already been noticed, th, tribution of tortoises approximates
to the former type, all the m '< -necked group being confined to the Southern
Hemisphere. Again, we find ..uit whereas Tropical Africa is closely related to



HABITS. I09

Tropical India as regards its Amphibians, while Australia and Africa are near
akin to South America in regard to their tortoises, in respect of lizards there is no
close connection between India and Africa, but an intimate relationship exists
between India and Australia, where members of the same genera occur ; while the
Australian lizards are totally unlike their South American cousins. As might have
been expected from their great numerical preponderance at the present day, lizards
appear to be a comparatively modern group, their remains being rare in the lower
Tertiary deposits, while in the Secondary period they are only known by a few
species from the rocks of the Cretaceous epoch. That the group has originated
from the tuateras, which were so abundant in the earlier strata of the Secondary
period, may be regarded as most probable.

Turning to their mode of life, we find that while a few members
Habits.

of the order resemble crocodiles, in spending the greater portion of

their time in water, visiting the land only for the purposes of feeding, sleeping,
or basking in the sun, by far the great majority of lizards are essentially land-
animals, avoiding even damp situations. Although some inhabit trees, the greater
number dwell either on the ground or among the clefts of rocks ; the conformation
of the body generally giving some indication of this diversity of habitat. Among
the land forms, for instance, those with depressed bodies are generally to be found
in open sandy deserts, where they seek shelter either beneath stones or in holes ;
whereas such as have the body compressed are more usually dwellers among
bushes or in trees. Those, again, in which the body is more or less cylindrical, are
in the habit of secreting themselves in the clefts of rocks or the chinks of tree-
stems; while the snake-like kinds live on the ground, and those with a more
worm-like form beneath its surface. The movements of the greater number of
species whether they live on the ground, among rocks, on trees, or on cliffs or
walls are agile in the extreme ; and while the majority run with their bodies
close to the ground, many habitually raise themselves up at times by resting on
their hind-legs and tails, and are able to spring, either on the ground or from
branch to branch, to a considerable distance after their prey. Of the arboreal
species, some make use of their tails to aid in maintaining their hold, while others,
together with cliff- and wall-hunting species, like the geckos, are enabled to run
along the under sides of boughs, or to ascend vertical surfaces by the aid of their
expanded and disc-like feet. The peculiar flying lizard is enabled to take long,
flying leaps, supported by a parachute-like membrane borne by the expanded ribs ;
while all the limbless species move somewhat after the manner of snakes, although
making less use of the extremities of the ribs. The few aquatic forms swim and
dive without the aid of webbed feet ; but mr ny other kinds swim w r ell if
thrown into water.

In many cases elegant and graceful in form, although at others rendered more
curious than beautiful by the presence of spines or warts, lizards are pleasing
rather than repulsive animals ; and, with the exception of the American heloderms,
none are poisonous, although some will bite sharp, , Few lizards possess a distinct
voice, the majority merely uttering a., low hiss; some, however, especially among
those whose habits are nocturnal emit a clear, sHrp cry, which has been likened
both to the scream of a frog, and to the chirp u. ,i cricket. Of their senses, the



j io LIZARDS.

most acute is doubtless that of sight, next to which probably comes hearing. In
regard to diet, a few lizards are strictly herbivorous, but the great majority are
more or less completely carnivorous; the larger kinds feeding on small mammals,
birds and their eggs, other reptiles, and, more rarely, frogs and fish, as well as
many descriptions of invertebrates. The smaller members of the order, on tin-
other hand, are restricted mainly or entirely to an invertebrate diet, the great
portion of which consists of insects, worms, and land-molluscs. Nearly all drink
by rapidly protruding and withdrawing the tongue ; dew affording sufficient
moisture to those living on rock or in trees, while some kinds can exist for long
periods, or even entirely without drinking. The species inhabiting the warmer
regions, save those which are arboreal or aquatic in their habits, pass the hottest
and driest season of the year in a state of torpor; while those in colder regions
regularly hibernate, such hibernation, in the case of some of the species inhabiting
the continent of Europe, lasting for a period of from six to eight months. As
regards their breeding-habits, the majority of lizards lay eggs, which may vary
from two to thirty in number, and have generally a soft and leathery covering,
although sometimes furnished with a hard calcareous shell.

One peculiarity characterising the members of the order cannot be passed
over before concluding these introductory remarks. This is the facility with
which they are enabled to reproduce lost parts, and more especially the tail. As
is well known, in many lizards, when handled, the tail breaks off without any
rough usage, and in all or nearly all |b will readily come in two if pulled when the
creature is seeking to escape, this susceptibility to automatic fracture being due to
a cartilaginous band across the middle of each vertebra of the tail in the case of
the common lizard of England. Such missing portion of the tail is speedily
reproduced, it may be double ; and whereas among the members of the typical
family of the order, the scaling of the reproduced portion is like the original, in
certain other forms this is by no means always the case. The remarkable circum-
stance about the matter is that when the pattern of the scaling of such a new tail
differs from the original, it always reverts to that characterising a less specialis
and probably ancestral group. It is scarcely necessary to mention that in sue
an extensive assemblage as the present, only a comparatively small percentage
species, or even genera, can be mentioned, and these but briefly.

THE GECKOS.
Family GECKONIDJE.

Few creatures have given rise to a greater amount of fable and legend than
the large group of lizards commonly known as geckos ; such legends being probably
due to the nocturnal and domestic habits of these creatures, coupled with the sharp
chirping cry from which they derive their name, and their curiously expanded
disc-like toes. Absolutely innocuous, they have been credited from the earliest
times with ejecting venom from their toes, and of poisoning whatever they crawled
over; while the teeth of one species have been asserted to be capable of leaving
their impression on steel. Indeed, so intense is the dread inspired by these little



GECKOS.



creatures, that in Egypt the lobe-footed, or Fan-footed species is commonly termed
abou-burs, or father of leprosy.

Geckos, of which there are some two hundred and eighty species, distributed
over all the warmer parts of the globe, although more numerous in the Indian and
Australian regions than elsewhere, are for the most part small and plumply-built
nocturnal lizards, characterised by their depressed form and dust-like coloration.
The rather long and more or less flattened head is broad and triangular in shape ;
the large eyes are characterised by the absence of movable lids, and by the pupil
jing, except in a few diurnal forms, vertical ; while the aperture of the ears is
:ewise in the form of an upright slit. Externally, the head is covered with minute
mules, or small scales, and the body is devoid of a bony armour, and in most
3es covered above with granules, and beneath with small overlapping scales. If
,-e add to the above features that the tongue is either smooth or covered with
illous papillae, and is short or
loderate in length, and not
leathed at the base, and that
le bodies of the vertebrae articu-
ite together by means of cup-
laped surfaces at both their
ttremities, we shall have said
ifficient to distinguish the
jckos from all other members
the suborder. As regards
leir other external characters,
neck is very short and thick,
body, although rounded,
larkedly depressed, and the
iil, which is generally remark -
)ly brittle, usually thick and




moderate length, with its



LOBE-FOOTED GECKO.



:',

lai





sal portion either cylindrical

laterally compressed, although it may be leaf -like, or even rudimental. In some
ses the tail is known to be prehensile, and it is not improbable that it is

quently endowed with this power. The limbs are generally remarkable for

eir shortness, and are always provided with five toes each, the tips or sides of
hich may be more or less dilated. In those species inhabiting desert regions, the
toes are of normal form, being often nearly cylindrical, and keeled on their lower
surfaces ; but in the great majority of the members of the family, they are expanded
either throughout their length or partially into adhesive discs, of which the under
surface is formed by* a series of movable symmetrical plates of variable form, by
the aid of which the creatures are enabled to ascend walls and run across the
ceilings of rooms. In some cases the claws are retractile, either within the plates

the discs, or into sheaths ; while in other instances the toes may be united by
ebs, which are not, however, for the purpose of swimming, all the geckos being
land-lizards. The numerous teeth are small, and attached to one side of the

mmit of the jaw (pleurodont).



TT2



LIZARDS,



Lobe-Footed The geckos being so numerous in species, which are arranged

Gecko. under no less than forty-nine genera, it is of course impossible in a
work like the present to do more than notice a few of the better known or more
striking. Among these, one of the most familiar is the little lobe- or fan-footed
gecko (Ptyodactylus lobatus), of Northern Africa, Arabia, and Syria. This is one
of two species belonging to a genus characterised by the toes (as shown in the




TURKISH GECKO (nat. size).

figure on p. Ill), being dilated at their summits, where they are furnished inferior!}
with two diverging series of plates ; the digits being furnished with claws capable
of retraction within notches in the front of the disc. The upper surface is cover
with granules, among which are some small keeled tubercles ; the colour beii
greyish or yellowish brown above, with darker and light spots, and below unifoi
white. The length is a little over 5 inches.
Turkish Gecko Equally well known is the Turkish gecko (Hemidactylus tur-

cicus), represented in the figure above, which is likewise a small



GECKOS. 113

species, inhabiting the countries bordering the Mediterranean and Red Seas,
and also found in Sind. It belongs to a group of genera with dilated toes and
compressed claws, and is specially characterised by the extremities of the toes
being free, the plates on the under surface of the discs arranged in double rows,
and the presence of some large shields on the under surface of the tail. Measuring
not more than 4 inches in length, this species may be distinguished from the other




FRINGED GECKO (nat. size).

European geckos by the body being covered with from fourteen to sixteen
longitudinal rows of warts, of which some are white and the others blackish, and like-
wise by the hue of the upper-parts being greyish brown spotted with flesh-colour.
It is, however, said to be able to change its colour according to circumstances, being
of a shining milky white at night, and dark-coloured during the daytime. The
genus to which it belongs comprises over thirty species, ranging over Southern
Europe and Asia, Africa, Tropical America, and Oceania.

VOL. V. 8



u 4 LIZARDS.

A larger and more remarkable species is the one represented in
*' the illustration on p. 113 (Ptychozoum homalocephalum), which
is the sole member of a genus characterised by the presence of an expansion of
skin along the sides of the body, continued as lobes on the tail, as well as by the
toes being completely webbed, and the inner one devoid of a claw. Attaining a
length of nearly 8 inches, this species has a distinctly ringed tail ; its colour above
being greyish or reddish brown, marked with undulating dark brown transverse
bands, and a dark streak extending from the eye to the first of the bands on
the back. This gecko is an inhabitant of Java, Sumatra, Borneo, and the Malay
Peninsula.

The last member of the family we shall specially notice is tin-
Wall-Gecko.

wall-gecko (Tarentola mauritanica), which is the Mediterranean

representative of a small genus ranging from the countries bordering the Mediter-
ranean to West Africa, and including one West Indian species. The genus is
readily recognised by all the toes being dilated, and only the third and fourth
furnished with claws. This species varies from rather less than 5 to somewhat
more than 6 inches in length, of which one-half is formed by the tail. The sides
of the neck and body, as well as the upper surface of the limbs, are ornamented
with conical tubercles ; the back carries seven or nine longitudinal rows of larger
and strongly-keeled tubercles ; and on the anterior half of the tail the ornamenta-
tion takes the form of knobs with backwardly directed spines. The general colour
of the upper-parts is greyish brown, with more or less distinct lighter and darker
marblings, while a well-marked dark streak passes on each side of the head through
the eye.

With the exception of a certain number of species, the geckos, as'
already said, are nocturnal in their habits ; and many are remarkable
for uttering shrill cries^ probably produced by striking the tongue against the!
palate, which in some cases are compared to the syllables yecko, checko, or toki, anc
in others to the monosyllable tok. A South African sand-gecko is at times stain
to occur in such numbers, and to produce such a din by its cry, as to render a
sojourn in the neighbourhood well-nigh insupportable. As regards their habitat-
geckos are very variable, some frequenting arid deserts, where they, in sonv;
instances, burrow in the sand ; others frequent wooded regions, living either among
low bushes or on trees, and concealing themselves during the day beneath stones
or the bark of the stems; others again are found among rocks; while a thin
group has elected to live among human dwellings, where some of its members h;m
become as fearless and confiding as domesticated animals. Of the arboreal species
the frilled gecko is peculiar in having a parachute-like expansion of skin, wliicl
is used after the manner of that of the flying squirrels in aiding its owner to ta
long leaps from bough to bough. When at rest, the parachute is kept close to tin
sides of the body by the aid of its intrinsic muscles ; and it is stated that tlii:
species, like several others, has the power of changing its colour according to tin
hue of the object in which it is resting. The species frequenting houses may 1
divided into those which resort to the interior, and those which are content will
the outside. Of the latter, Sir J. E. Tennent writes that in Ceylon, "as soon a
evening arrives, geckos are to be seen in every house in keen and crafty pursuit o



GECKOS.



their prey ; emerging from the chinks and recesses where they conceal themselves
during the day, to search for insects that then retire to settle for the night. In a
boudoir, where the ladies of my family spent their evenings, one of these familiar
and amusing little creatures had its hiding-place behind a gilt picture-frame.
Punctually as the candles were lighted, it made its appearance on the wall to be
fed with its accustomed crumbs ; and, if neglected, it reiterated its sharp quick call




WALL-GECKOS (nat. size).

of chic, chic, chit, till attended to. It was of a delicate grey colour, tinged with*

pink ; and having by accident fallen on a work-table, it fled, leaving part of its

tail behind it, which, however, it reproduced within less than a month. ... In an

officer's quarters, in the fort at Colombo, a gecko had been taught to come daily to

I the dinner-table, and always made its appearance along with the dessert. The

I family were absent for some months, during which the house underwent extensive

repairs, the roof having been raised, the walls stuccoed, and the ceilings whitened.

It was naturally surmised that so long a suspension of its accustomed habits would



n 6 LIZARDS.

liave led to the disappearance of the little lizard ; but on the return of its old
friends, it made its entrance as usual at their first dinner, the instant the cloth was
removed." Another Indian observer, Colonel Tytler, writing of these house-geckos
states that although several species " may inhabit the same locality, yet, as a
general rule, they keep separate and aloof from each other; for instance, in a
house the dark cellars may be the resort of one species, the roof of another, and
the crevices in the walls may be exclusively occupied by a third species. However,
at night they issue forth in quest of insects, and may be found mixed up together
in the same spot ; but on the slightest disturbance, or when they have done feeding,
they return hurriedly to their particular hiding-places." So far as is known, all
the members of the family agree with the house-geckos in being insectivorous.
With the exception of two peculiar New Zealand species producing living young,
all the geckos appear to lay eggs, which are enclosed in a round and hard shell,
and are generally two in number.



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 13 of 62)