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to voluntarily undergo long fasts. While in the water it has been observed to







IPPI SALAMANDER (\ nat. size).



nake the air from its lungs pass over the gills, with the apparent object of more
ully oxygenating the blood in the latter.

Three Toed The eel -like or three -toed salamander (Amphiuma means)

Salamander, represents another North American genus, ranging from the Mississippi
o South Carolina, and distinguished by its extremely elongated and eel-like form,
nd the small size of the limbs, each of which terminates in three or two minute
oes. The tongue is indistinctly defined, covering the whole of the floor of the mouth,
j which it is everywhere adherent ; there is a gill-aperture on each side of the neck,
nd four internal gill-arches are present. The head is relatively small, with a rather
3ng and narrowing muzzle, at the extremity of which are the small and widely-
Bparated nostrils ; the eyes are likewise minute ; the lips are unusually thick and
eshy ; and the short compressed tail is keeled superiorly. The smooth and slimy

VOL. V. 20



306



NE WTS AND S, iLAMA XHERS.



skin is of a uniform blackish brown colour, although rather lighter below than
above. In total length, full-grown examples measure about 31 inches. From the
difference in the number of the toes it has been thought that there are two species ;
but since the two-toed and three-toed forms are in other respects similar, it seems
preferable to regard them as varieties or local races of a single species. Thr.M-
salamanders are inhabitants of muddy waters, frequently burying themselves in
the mud at the bottom, in one instance to the depth of a yard or more, in thick
clayey mud of the consistence of putty, in which they burrowed like worms. They
also frequent the irrigation channels in rice-fields, while they occasionally venture




THUEE-TOED OK EEL-LIKE SALAMANDER (^ liat. size).



on land. Their food comprises fresh-water mussels, fish, beetles, other insects, an
crustaceans. Beyond the fact that the female lays eggs, in which the tadpole lie
coiled up until it attains several times the length of its chamber, little is known a
to the breeding-habits of this species.

THE GILLED SALAMANDERS.
Family PROTEIDJE.

Represented only by the curious olm of the subterranean waters of Carniol
and other parts of Europe, and by an allied genus in North America, the gille*
salamanders take their title from the permanent retention of external gills, (X
which account they may be regarded as some of the lowest representatives of tE



GILLED SALAMANDERS.



37



order, In addition to this primary feature, they are characterised by the absence
of the upper jawbone or maxilla, although the premaxilla is present, and, like the
lower jaw, furnished with teeth. There are no eyelids, and the bodies of the
vertebrae are cupped at both extremities. There are differences in the external
form of the two representatives ; the olm being a long, snake-like creature with
small limbs, whereas the American species resembles a salamander.

Olm Known for more than a couple of centuries, the remarkable

creature to which Oken gave the name of olm is the sole representa-
tive of its genus, and is technically known as Proteus anguineus. From its American
ally it is distinguished by its elongated snake-like body and small and widely





separated limbs, of which the front pair are provided with three, and the hinder
with only two toes. The eyes are concealed beneath the skin, the small tongue is
free in front, and the palatal teeth are small and arranged in a double series. In
the typical form from Carniola the head is elongate, with a long and narrow
muzzle, truncated at the tip ; the mouth being small, with large lips. The short
and much compressed tail is provided with a fin, and rounded or bluntly pointed
at the tip. The smooth skin is marked by twenty-six or twenty-seven grooves,
corresponding to the ribs, and is uniformly flesh-coloured, with coral-red gills. In
a variety from Dalmatia the snout is longer and narrower, and the number of
' costal grooves only twenty-four ; while in a second variety, inhabiting Carinthia,
the whole form is stouter, the head shorter, with a rounded muzzle, and the
number of costal grooves twenty-five. There is also a certain variation as regards
colour, apparently largely depending upon the amount of light to which the
creatures have been exposed ; some examples being reddish brown, and others
darker with bluish black spots. The usual length is about 10 inches.



308 NEWTS AND SALAMANDERS.

Totally blind, the olm is found solely in the subterranean waters of the
caverns of the Alps of Carniola, Dalmatia, and Carinthia ; and has long been an
object of the greatest interest to naturalists. It has been thought that the waters
in which the olm lives were all connected together underground, and that the
creatures only came up during flood-time ; but the great distance from one another
of the various localities where they are found is somewhat against this view.
It is, however, only when the subterranean waters are at their greatest height that
the olms are captured by the peasants, by whom they are placed in glass jars, half
filled with water and sold to tourists. In confinement, where they have been
known to survive from six to eight years, they lie sluggishly all day at the bottom
of their tank, only moving if a ray of light impels them to seek a darker corner.
When in small vessels, where the water is not often renewed, they will frequently
come to the surface to breathe, opening their mouths, and letting air pass through
their gill-openings; but in deeper, or frequently changed water, they breathe
entirely by means of their gills. Many experiments have been made, with the
view of ascertaining whether the olm will, under any circumstances, lose its gills,
but hitherto without result. In captivity the food of these amphibians consists of
molluscs, worms, and the minute creatures to be found among the leaves of water-
plants. In spite of having been kept for many years in captivity, it was not
ascertained till 1875 that the olm lays eggs; and it was thirteen years later before
any tadpoles were hatched in captivity, In April 1888, upwards of seventy-six
eggs were laid by a single female ; and after a period of three months developed
into tadpoles. These were very similar to the adult, but the tail-fin extended
three-quarters down the back ; the eye was larger, and apparently more susceptible
to light ; and the hind-limbs were in the form of small knobs.

Furrowed A very different looking animal is the furrowed salamander

Salamander, (Necturus maculatus), of Eastern North America and Canada.
which takes its name from the strongly - marked fold of skin on the throat.
In addition to its shorter and more lizard-like form, and relatively longer limbs, it
differs from the olm by having well-developed eyes, and four toes to each foot.
The tongue is large, with the front border free ; and the palatal teeth are large
and form a single series. In colour the smooth skin is brown, with more or less
well-defined circular blackish spots, and lighter on the under-parts than on the back.
The total length is about a foot. An allied species (N. punctatus) inhabits the rice-
fields of the Southern States. The food is similar to that of the allied forms, and
in winter these salamanders seek protection from frost by burrowing deep in the
mud. They come at times to the surface to breathe, and will even venture on land;
but they chiefly respire by means of their gills, and if the latter become entangled,
they are carefully rearranged by means of the fore-foot.

T \VO-LEGGED SALAMANDERS.
Family SiRENW^;.

The sole representatives of this, the last, family of the Tailed Amphibians arc
the two-legged salamanders of North America, of which there are two speciesi
arranged under as many genera (tfiren and Pseudobranchud). While agreeing;



TWO-LEGGED SALAMANDERS.



39



with the preceding family in the permanent retention of external gills, they are

distinguished by the total loss of the hind-lirnbs, and likewise by the absence of

teeth in the margins of the jaws. The siren salamander (Siren lacertina), which

inhabits the South-Eastern United States, may be compared to a snake furnished

with a pair of short fore-legs and external gills ; and is especially distinguished by

the presence of three pairs of

gill-openings on the sides of

the neck and the four-toed feet.

The smooth skin is either

uniformly blackish, or marked

with small white dots, and the

total length reaches to as much

as 28 inches. The Georgian

two-legged salamander (Pseu-

dobranckus striatus), on the

other hand, has only a single

pair of gill - openings on the

neck, and but three toes to

the feet. These salamanders

are stated to frequent swampy

localities, especially pools of

water beneath the roots of old

trees, up the stems of which

they will sometimes climb. A living example was received in England in 1825,

where it lived till 1831. This specimen was fond of coming out of the water to

rest on sand or among moss ; and in summer ate worms, tadpoles, and various

other small creatures, but became torpid from the middle of October till the end

of April. That these salamanders can breathe entirely by means of their lungs,

is proved by a specimen in an aquarium whose gills had been eaten off by a fish.




SIREN SALAMANDER.



THE CCECILIANS OR WORM-LIKE AMPHIBIANS.
Order APODA.

The remarkable worm-like and blind amphibians forming this group are
erally regarded as the representatives of a distinct order ; although they are
sidered by Professor Cope to be merely a degraded branch of the Tailed
Amphibians, to which they are allied through the fish-like salamanders. Be this
as it may, the group is readily distinguished by the total absence of limbs, and the
general worm-like appearance of the head and body ; the tail being either
rudimental or wanting. In the skull the frontal bones are distinct from the
parietals, but the palatines are fused with the maxillae. As regards their
reproduction, these amphibians differ from the newts and salamanders in that the
two sexes come together in the ordinary manner. Some of them are peculiar in
having overlapping scales embedded in the skin, like fishes ; and in all the eyes
are either wanting, or are so deeply buried beneath the skin as to be entirely



3 io



NEWTS AND SALAMANDERS.



useless. The whole of the members of the group are burrowing in their habits ;
and in the adult state are completely terrestrial, laying eggs from which are
developed gilled tadpoles that do not take to the water till some time after birth.
The fourteen genera into which the group has been divided may all be included in
the single family Coeciliidce. Geographically, these amphibians are spread over
the Indian region, Africa south of the Sahara, and Central and South America ;
but it is not a little remarkable that they are quite unknown in Madagascar,
although two species occur in the Seychelles.

They may be divided into two main groups, from the presence or absence of
scales in the skin ; two of the best known representatives of the group in which
scales are developed, at least in some portion of the body, being the Oriental
Ichthyophis and the South American Ccecilia; one of the species of the latter
genus being represented in our illustration. The common Cingalese species
(Ichthyophis ghtiinosus), which ranges from Ceylon and the Eastern Himalaya to




A WORM-LIKE AMPHIBIAN, Ca'cilid (liat. size).

Sumatra and Java, inhabits damp situations, and usually burrows in soft mud.
In some hollow near the w r ater, the female (which measures about 15 inches in
length), lays a cluster of very large eggs, round which she coils her body, am
proceeds to brood them after the manner of a python. After the young ai
hatched out they remain in the egg-moss until they have lost their external gill
after which they take to the water, to lead for a time an aquatic life. During thi
stage of their existence the head is fish-like, with large lips, and the eyes l>< ; tt
developed than in the adult ; and they have a gill-opening on each side of tl
neck, and the tail is distinct^ defined, much compressed, and furnished both alxn
and below with fin. Of the group without scales, the genus Gegenophis is fror
Southern India, Siphonope from Tropical America, and Typhlonectes and Chthont
petum from South America-




SKELETONS OF PRIMEVAL SALAMANDERS.

Protriton, A, and Pelosaurus, B. (From Credner ; much enlarged.)



CHAPTER III.
THE PRIMEVAL SALAMANDERS, Order LABYRINTHODONTIA.

THE remaining amphibians are extinct, and form an order mainly characteristic
of the upper Palaeozoic and Triassic periods, but also lingering on into the
Jurassic. They derive their name of Labyrinthodonts from the complex structure
of the teeth of the higher forms ; these displaying a peculiar pattern, caused by
infoldings of the outer layer, which penetrate nearly to the centre of the crown
in festooned lines. Most of these creatures have the general form of a salamander,
with the front-limbs shorter than the hinder-pair ; the latter having always five
Itoes, although in the former the number may be reduced to two. Their most
characteristic feature is, however, to be found in the structure of the skull, in
which the bones are generally covered with a pitted or radiated sculpture,
somewhat similar to that of crocodiles. From the accompanying figure of the
skull of the mastodonsaur, it will be seen that the whole of the upper surface
behind the sockets of the eyes is covered by a complete bony roof, extending
continuously from the bone marked P, which immediately covers the brain-cavity
to the sides of the hinder-part of the jaws (QJ), whereas in all the modern
[usalamanders this region is more or less open. This roofed skull of the
primeval salamanders presents an approximation to the earlier fishes; and a
ivscmblance to that group is also shown by the paired supraoccipital bones (So),



PRIME VAL SALAMANDERS.




which in all the higher Vertebrates are fused together. Nearly all these
salamanders are further distinguished by having the chest protected by three

sculptured bony plates, one of which is central
while the other two are lateral ; the position of
these plates being shown in our figure of the
skeleton, where they are seen on the lower surface
of the body, immediately behind the head, under-
lying the backbone and ribs. Besides this armour,
some species had the whole of the under surface
of the body protected by a series of bony scales,
arranged in a chevron pattern ; while in a few
instances similar scales also invested the upper
surface of the body. The majority of the meml < TS
of the order had the vertebrae of the backbone in
the form of simple doubly-cupped discs, similar to
those of fishes ; but in some of the most primitive
types each vertebra consists of four distinct pieces,
namely, a single basal piece (i), a pair of lateral
pieces (pi), and a single arch and spine (s). Among
some reptiles the basal piece remains between
two adjacent vertebrae as the intercentrum ; but
in the higher forms the other elements coalesce.
Since a similar type of vertebra occurs in certain
extinct fishes, we have in this structure another
bond between the latter and the primeval sala-
manders. Brief reference must also be made to the small aperture in the roof
of the skull of the primeval salamanders in the bone marked P, since this corre-
sponds to one in the skull of the tuatera lizard of New Zealand. In that animal
the aperture overlies the rudiment of an
eye sunk deep down in the brain and now
totally useless, but probably functional in
the tuatera's ancestors. The large size of
the aperture in the primeval salamanders
suggests that the central eye may still have
been capable of receiving impressions of
light, although we may have to go back to
earlier forms before it was of any functional
importance as an organ of vision. As in
many existing amphibians, teeth frequently
occur on the bones of the palate as well as
in the margins of the jaws. Another feature
of the skulls of many members of the order
is the presence of what are called mucous

canals in the bones of the upper surface, as shown both in the accompanying figui
and in the one on p. 313 ; these canals also occurring in certain fishes. So far
can be ascertained, both external and internal gills generally disappeared in



SKULL OF THE MASTODONSATJR, WITH THE
SCULPTURE OMITTED.

SO, supraoccipital ; Ep, epiotic ; P,
parietal ; Sq, squainosal ; ST, supratem-
poral ; QJ, quadratojugal; Ju, jugal ; Pt,
postfrontal ; PtO, postorbital ; Fr, frontal ;
PrF, prefrontal ; L, lachrymal ; Na, nasal ;
MX, maxilla. The premaxilla has no letter.
(About | nat. size.)




TWO VERTERK.K OF A 1'HIMEV.U, SALAMANDER.

prz is the anterior and ptz the posterior end.



PRIMEVAL SALAMANDERS.



the adult. Varying from the size of a small newt to that of a crocodile, the
primeval salamanders are of especial interest to the evolutionist, as it is pretty
certain that not only are they the descendants of primeval fishes, but that
they are the ancestors both of the modern Amphibians and the extinct Anomodont
Reptiles. And it is probable that Mammals have originated, either directly from
them or from a lost group intermediate between them and the Anomodont
Reptiles. They appear to have been spread over the whole globe, and they have
been divided into several subordinal groups. Among
these the highest are the true Labyrinthodonts,
typically represented by the gigantic Mastodonsaurus
and the somewhat smaller Metvposaurus of the Trias.
These were crocodile -like animals, generally with
disc-like vertebras in the adult, the teeth more or
less plicated, and the surface of the skull marked
with sculpture and mucous canals. In the Permian
mrchegosaurus, the vertebras were, however, of the
complex primitive type. The Gilled Labyrinthodonts,
as represented by Protriton and Pelosaurus, are a
group of much smaller forms, characterised by their
barrel-shaped vertebras, pierced by a remnant of the
canal of the primitive notochord ; short and straight
ribs, articulating by a single head ; simple teeth, and
the absence of ossification in the occipital region of
the skull, as well as in the wrist and ankle-joints; a

further point of distinction being the development of internal gills in the young.
The Permian and Carboniferous Snake-like Labyrinthodonts are characterised by
the snake-like form of the body, and the apparent absence of limbs. The vertebras
were elongated and without spines, while the ribs were slender and barbed like
those of fishes, and the teeth smooth and simple. Probably the external gills
persisted throughout life. In Britain the group is represented by the small
Dolichosoma ; but Palceosiren of Bohemia is estimated to have been over 40 feet
ig. If these creatures prove to be the ancestors of the Worm-like Amphibians,
it would show that the latter are distinct from the newts and salamanders. The
Microsauria, include small lizard-like forms, such as Ceratoerpetum and Hylonomus
from the Carboniferous of Europe and Nova Scotia, which appear more highly
organised than the preceding, and thus connect the Amphibians with the Beaked
Reptiles. Their vertebrae are long and constricted, with traces of the notochord ;
the ribs are generally long, curved, and two-headed ; the teeth have large central
pulp-cavities, but no plications ; the occiput is ossified ; but the wrist and ankle are
either ossified or cartilaginous ; and in some cases the back is covered with bony
scales. In several forms the bony scales on the under surface are so slender as to
assume the appearance of abdominal ribs like those of the Beaked Reptiles.




SKULL OF THE METOPOSAUR

(J nat. size).




FISHES.



CHAPTER I.
GENERAL CHARACTERISTICS, Class Pisces.

ALTHOUGH in popular language lampreys are included among fishes, while unti
quite recently the lancelet was very generally placed by zoologists in the sai
class, it now seems preferable to make each of these the representative of a distinc
class, and the true fishes can consequently be defined with greater precision. Ii
this somewhat restricted sense fishes may be described as cold-blooded vertebrat
animals, adapted for a purely aquatic life, and breathing almost invariably
means of gills alone. They have a heart consisting generally of only two chambei
(three in the lung-fishes) ; the limbs, if present, are modified into fins ; there ai
unpaired median fins, supported by fin-rays ; and, as in all the higher classes, t\
mouth is furnished with distinct jaws. The skin may be either naked, or coverc
with scales or bony plates. As a rule, fishes lay eggs; and the young do nt
undergo a distinct metamorphosis.

With the Tailed Amphibians the class is very closely connected by means
the lung-fishes, which are furnished not only with internal gills, but likewise wit
functional lungs, and during the early part of their existence with external i
while these fishes also differ from the other members of the class in that the nostril
communicate posteriorly with the cavity of the mouth, as in the higher Vertebrate



GENERAL CHARACTERS. 315

Although the bony fishes of the present day form a specialised side-branch, which
has lost many of the characters common to the two classes, it will be evident that
Fishes and Amphibians are very closely allied groups ; the latter of which has been
directly derived from the former. Geologically, fishes are older than any of the
classes hitherto described, their fossil remains occurring in strata belonging to the
upper part of the Silurian division of the Palaeozoic epoch.

The form of a typical fish is so well known that it will be quite unnecessary
to describe it ; and it may be mentioned that this typical form, which is the one
best adapted for progress through water, is very general amongst fresh-water fishes,
although the eels constitute an exception in this respect. Much greater diversity
exists, however, among the marine representatives of the class ; and we may cite
ias extreme types a shark, a flat-fish, a ribbon-fish, and a globe-fish.

The structure of the skeleton, both external and internal, being
Classification. . . . . .

of the utmost importance in the classification of fishes, it is essential

Sthat the attention of the reader should be more fully directed to this point than
thas been done in the case of the higher Vertebrates. It should first be mentioned
that fishes are divided into four subclasses, namely, the Lung-Fishes or Dipnoi ; the
Chimaeroids, or Holocephali ; the Bony Fishes and Ganoids, or Teleostomi ; and the
Sharks and Rays, or Elasmobranchii. These may be further subdivided into orders
as follows :

1. Lung-Fishes Subclass DIPNOI.

(1) True Lung-Fishes Order SIRENOIDEI.

(2) Berry-Boned Fishes Order ARTHRODIRA (extinct).

2. Chimseroids Subclass HOLOCEPHALI.

3. Bony-Fishes and Ganoids Subclass TELEOSTOMI.

(1) Fan-Firmed Fishes Order ACTINOPTERYGII.

(2) Fringe-Finned Ganoids Order CROSSOPTERYGII.

4. Sharks and Rays Subclass ELASMOBRANCHII.

(1) Acanthodians Order ACANTHODII (extinct).

(2) Fringe-Finned Sharks Order ICHTHYOTOMI (extinct).

(3) True Sharks and Rays Order SELACHOIDEI.

External In regard to the external skeleton, the most characteristic type

jeieton. takes the form of scales. When these overlap and their posterior
ler is entire, such scales are termed cycloid, but when serrated, ctenoid. The
xternal skeleton may. however, take the form of plates or granules, which in the
himasroids and sharks and rays are generally isolated, and have a structure
precisely similar to that of teeth, consisting of a base of ivory or dentine capped
vith enamel. The so-called ganoid scales, like those of the bony-pike, are, on the
Dther hand, quadrangular, and often connected by a peg-and-socket arrangement ;
-hey are formed of true bone capped with an enamel-like substance termed ganoin,
md true bone likewise occurs in the plates of the sturgeons. A series of specially
nodified scales, running along the sides of many fishes, constitute the so-called
ateral line, which is partly connected with the supply of mucus ; and certain large
^-shaped scales on the borders of the fins of many extinct bony fishes are known
is fulcra. The fin-rays, which also come under the designation of dermal structures,



316



FISHES.




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Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 33 of 62)