traces of closely-set endoplasts are discover-
able. The inner (Jig. 317. E, d) " striated
membrane " is a membrane having a similar
structure, possessing similar relations to the
inner surface of the feather, and which is con-
tinuous with the so-called "pith" in the quill
of a fully formed feather. The mode of de-
velopment of these rootsheaths is identical
with that of those in the hair, and therefore
requires no further elucidation here.

Tegumentary glands. The other con-
versionary productions of the ecderon which
we have to consider, are the glandular ap-
pendages, which are always diverticula of
the cellular ecderon inwards.* Under this
head I include only those small glandular
organs which, so far as we know, have no
reference to any other functions than that of
cutaneous transpiration or fatty secretion,
referring to the articles on special divisions
of the animal kingdom for an account of
those organs, such as the " water vessels " of
Echinoderms and Trematoda, the nidamental
glands of Mollusks, the genital glands of
Vertebrata and Insecta, which might strictly
be regarded as productions of the integument.

Tegumentary glands in this limited sense
are somewhat rare among the Invertebrata.
They have, however, been observed in the
Annelids, where they consist of delicate tubes,
terminating internally by a blind extremity
containing a single nucleated cell. Such
glands exist on the ventral surface of the head
and foot discs in Piscicola, and are scattered
all over the body in Clepsine and Nephelis.
Similar glands are found opening upon the
ventral surface of Argulus foliaceus.

* Unless, indeed, these simple " mucous cells,"
described by Clark and Leydig in Fishes, and
which are merely modified cells of the cellular
ecderon, should be regarded as glands.

K K 2



500



TEGUMENTARY ORGANS.



Simple coecal glands are scattered over the
whole surface of the body of the Procession
Caterpillars, opening at the points of the hairs ;
on the sides of the body in Myriapods. on the
joints of the legs in Beetles and Bugs.

In Mollusca a peculiar, probably glandular,
canal exists in the foot of certain Lamelli-
branchs, and glandular coeca have been ob-
served in the lower surface of the foot in
Paludina. A ciliated canal runs in the foot
of Pulmonata, and receives glands on each
side. The existence of cutaneous glands in
the Cephalopods appears doubtful at least,
H. Miiller could only find them as shell
glands in the expanded arms of Argonauta.

Among the Vertebrata, Fishes, Ophidia,
Chelonia and Birds, appear to possess no
proper cutaneous glands * ; in Sauria they
attain a very slight and local, but in
Batrachia and Mammalia, an immense de-
velopment. In the frog, the whole surface

Fig. 318.




The cutaneous glands of the Frog.
A, section ; B, superficial view.

of the ecderon is beset with minute trifid
apertures, so disposed between three epi-
dermic cells, as to present a singular resem-
blance to the stomata of plants (Jig. 318. B).
These lead directly into spherical sacs (fig.
318. A. d.), which are lined by a continuation of
the cellular ecderon, and lie in the superficial

* Dr. Clark, in his excellent account of the skin
of the eel (Trans. Mic. Soc. 1849), describes cuta-
neous glands in that animal. The so-called " glands "
of the lateral line, however, have since been shown
by Leydig to have a very different structure ; and
I confess I have not been able to convince myself of
the existence of the other glands described'by Dr.
Clark. I can find nothing like them, except the
strong perpendicular semi-elastic bands, which tra-
verse and unite the bundles of connective tissue in
this as in other fishes.



part of the enderon above its stratified layer
(Jig. 318. A. g.) (vide infra). Nerves (/)
and vessels penetrate the latter to reach the
superficial layer of the enderon, and ramify
among these close-set glandular sacs. The
sacs usually contain only a clear fluid * ; they
are contractile, and may be made to expel
their contents by irritation of the nerves dis-
tributed to them.f

In Mammals, we meet with two kinds of
cutaneous glands, sebaceous and sudoriparous.
The former are almost invariably developed
in connection with the hair sacs, consisting
in fact of diverticula of the Malpighian layer
of the cellular ecderon of the upper portion
of these sacs, whence their position is always
superficial. The innermost cells of the solid
process become filled with fat break down,
and pour their contents into the hair sac
itself, by whose aperture they make their exit.
Sometimes, as in the hairs of the head in man
and in the pig's bristles, the sebaceous glands
are very small and simple, while in other lo-
calities they throw out processes, and assume
the appearance of complex racemose glands,
disposed like rosettes around the hair-sac,
from which they are developed.

Sudoriparous glands. These glands, like
those just described, are, as Gurlt pointed out,
simple, elongated processes of the deep layer
of the ecderon, differing from the sebaceous
glands chiefly in producing a clear fluid, instead
of a fatty secretion. As Kolliker has shown,
however, no line of demarcation is to be drawn
on this ground, the secretion of the axillary
sudoriparous glands in man being an essentially
sebaceous substance. The sudoriparous glands
are cylindrical coecal tubes varying, in man, from
TOO to -s&o f an mcn m diameter, whose walls
are either thick or thin. In the former case
they consist of a simple ecderonic cellular coat,
contained within a prolonged sheath, formed by
the uppermost layer of the enderon, and, like
it, composed of a homogeneous or indistinctly
fibrillated periplast, with imbedded endoplasts.
Outside this, or rather forming part of it, is a
layer of longitudinally-disposed smooth mus-
cles, and the whole is coated, like the deep sur-
face of the rest of the enderon, by a more or
less distinct layer of connective tissue. In
the thin-coated glands the muscular layer is
absent, but the cellular ecderonic coat is fre-
quently so thick that they possess no cavity at
all. The thick-walled glands are met with in
man in the axilla, scrotum, anal region, &c. ;
while those of the rest of the body are al-
most entirely of the thin- walled description.
The glands terminate superiorly in undu-
lating canals, which reach the surface of the
enderon, and are continued to that of the
ecderon by oblique channels excavated in its
substance between its cells. Inferiorly, they
form close coils, which lie in the subcutaneous



* Stated by Bergmann and Leuckart to have an
irritating property in Triton.

t Ascherson : *Haut-driisen d. Frosche, Miiller's
Arrhiv, 1841. Czermak : Haut-nerven d. Frosche
Ibid. 1849.



TEGUMENTRAY ORGANS.



501



areolar tissue, and receive twigs from the
vessels in their neighbourhood.

In the other Mammalia, the general structure
of the sudoriparous glands is as in man. In
the sheep, according to Gurlt,they present the
same coiled arrangement, while in the ox and
dog they are straight and simple. In the ox
they have rounded, d.lated extremities, and
are everywhere similar in shape and size. On
the hairy parts of the body of the dog, they
are small simple coeca, which are very difficult
to discover ; while on the ball of the foot of
this animal they are very large and resemble
those of man. Very large sudoriparous glands
have likewise been observed upon the horse's
prepuce.

Scales of fishes. In the Ganoid fishes Ac-
clpenser and Polyptertu the substance of the
scales is composed of ordinary bone whose
superficial layer is only denser than the rest,
and exhibits a local developement of fine
branching tubuli ; but in other fishes, two, if
not three, distinct layers are usually distin-
guishable in the scales.

In many Plagiostomes, for instance, the
placoid scales have the same composition as
the teeth, consisting of a superficial layer of
nearly structureless dense " enamel," or as
Prof. Williamson more conveniently terms
it, " Ganoin," while the deeper substance is
composed of a tissue in every respect similar
to dentine, whose innermost portion in some
cases passes into true bone, an addition
which might be compared to that of the
cement in the teeth. Leydig, indeed, has
shown that the resemblances between the
scales and the teeth of Placoid fish extend
even to their mode of developement. If the
pulp contained in the central cavity of the
spine-like scale of a Raia clavata be pulled
out, globular calcareous masses of T Q^ of an
inch and upwards in diameter, and either
solitary or adhering together in masses, will
be found to be attached to its surface. " These
globules are exactly analogous to the dentine
globules described by Ozermak, which in
human teeth afford the formative material for
the matrix of the dentine. What, however, ap-
peared to me especially worthy of notice
was the circumstance, that the most distinct
and beautifully branched canals, having exactly
the same appearance as those in the substance
of the spine, were already visible in these
isolated calcareous bodies, and on carefully
examining the fine processes of the canals,
no doubt could exist that they were only
interspaces or gaps. On carefully adjusting
the focus, in fact, it was obvious that one of
these large calcareous globules is itself only
an agglomeration of many smaller globules,
and it could be observed that the gaps left
between the latter became the fine processes
of the tubules. From these facts, I believe
that the correct mode of conceiving the
growth of the substance of the spine is, to
suppose that the calcareous matter is excreted
from the vessels of the pulp, and then in all
probability combined with organic matter,



runs into smaller masses ; these unite together
into larger ones, and become applied to the
inner surface of the central cavity, coalescing,
and thus adding to the thickness of the spine.
Between the calcareous globules, however,
canalicular gaps or tubules' remain, which
form a connected network and communicate
with those branched cavities which already
exist in the spine.

The scales of the Sharks and the dermal
spines of the Rays, then, (and I would draw
particular attention to this result,) are per-
fectly identical in structure with the teeth,
even to the absence of nerves in the pulp,
and must be united in the same structural
group. I have already (On the Skin of Fresh-
water Fishes, Zeitschrift fiir Wiss. Zool. B.
iii. H. 4.) pointed out the close affinity be-
tween the scales of a number of osseous
fishes and their teeth : and scales likewise
present globules of calcareous matter, which
become fused together to form the homo-
geneous substance of the scale. A process,
corresponding with that which occurs at the
surface of the pulp in the teeth and cutaneous
spines, here takes place from the surface of
the sac of the scale (Schuppentasche). The
scales of osseous fishes, the spines of the
Rays, and the scales of the Sharks, therefore,
all belong to the series of dental structures,
which in no respect interferes with the en-
trance of true bony tissue (like the " cement "
in the higher animals) into their composition,
as we find to be the case in the scales of the
Ganoids (Miiller), and in the truly bony semi-
canals which are attached to the scales of the
lateral lines of many fishes." *

For the details of the various modes in which
Ganoin, true osseous tissue, and those va-
rieties of tubular, more or Jess dentine-like
tissues, to which Prof. WilliamsoiP has given
the names of " Lepidine and Kosmine," are
combined together in the scales of Ganoid
and Placoid fish, I must refer to that gentle-
man's memoirs, already so often cited.

In the Ctenoid and Cycloid fishes there is
a superficial " Ganoin " layer, composed of
numerous thin structureless calcified laminae,
which are frequently thrown into folds, papillae
or spines. The deeper substance of the scale
is composed of a series of layers of a mem-
branous substance, each layer being composed
of parallel fibres which take a different direc-
tion from those of the superficial and subse-
quent layers, so that the fibres of alternate
layers cross diagonally. No endoplasts or
cells are ever distinguishable among the fibres.
In the deepest part of the scale these layers
are entirely membranous ; but in passing to-
wards the surface, minute lenticular masses
of calcareous matter make their appearance
in the membranous substance. As Prof.
Williamson justly states, these lenticular bodies
are not developed between the membranous
fibres and lamellae, but in them : " they com-
mence as a small calcareous atom, and in-.

* Leydig : Rochen und Haie, 1852,
K K 3



502



TEGUMENTARY ORGANS.



crease in size by the external addition of new
concentric lamina?; the direction of the latter
not beingparallel with, or having any reference
to, that of the laminae of fibrous membrane
with which they so amalgamate; thus they
are not depositions from, but growths in the
membrane ; which growths, as they increase
in size, retain their primitive tendency to
assume a lenticular form." Following the
layers of the scale outwards, these isolated
calcareous deposits not only enlarge, but
ultimately become fused together, forming at
length either a continuous calcareous mass in
each layer, or presenting fissures which in
some cases traverse the original lenticular
calcareous deposits, in others are interstitial
to them. I think one cannot but be struck
with the complete analogy between the struc-
ture and mode of developement here described
and those which I have previously shown to
obtain in the calcified tegumentary organs of
the Mollusca and Crustacea. The ganoin
layer corresponds very closely with the " epi-
dermis " of the shell or test ; the middle
laminated calcified substance is formed by the
fusion of concentrically laminated concretions
deposited in a membranous matrix in the
Fish, the Mollusk, and the Crustacean alike ;
while the deep uncalcified layers of the scale
are represented by the " horny " laminae which
have escaped calcification in Haliotis or Unio,
and still more closely by the fibrillated un-
calcified layers of the Crustacean test.

Structure of the enderon. The enderon of
the Invertebrata is usually entirely composed
of rudimentary connective tissue or of mere
indifferent tissue, consisting, in the latter case,
simply of a matrix with imbedded endoplasts,
while in the former it is produced into plates
and bands, never exhibiting, however, the pe-
culiar bundles and elastic fibres which are met
with in fully formed connective tissue.

In Paludina, according to Leydig, the pig-
ment masses, which lie on the surface of the
ecderon, are connected by " clear large cells,
with a small parietal nucleus." From their
occurrence, wherever in the higher animals
connective tissue is found, Leydig calls them
'* Binde-substanz-zellen " " Connective tissue
cells ; " but, as he himself points out, they fre-
quently contain carbonate of lime, and their
relation is rather, like that of the similar cells
in Piscicola, to fat.

A wonderful complication of structure is
attained by the skin of the Cephalopoda. Ac-
cording to H. Miiller *, who has recently made
some careful investigations on this subject, there
lie beneath the cellular ecderon in these ani-
mals : 1st, a fibrous layer, usually colourless,
but occasionally white and glittering. 2nd, the
layer with the chromatophora (vide inf.). 3rd,
beneath these a peculiar layer, which gives rise
to the colours produced by interference, the
metallic lustre, and intense whiteness of many
localities. It consists frequently of regular
plates, which evidently proceed from nucleated
cells. 4th, deeper still lie the larger bundles

* Bericht, &c. Zeitschrift fur Wiss. Zoologic.
1853.



of connective tissue, the muscles and the
vessels.

In the Vertebrata, the superficial layer of
the enderon is similarly composed of indifferent
tissue, and of rudimentary connective tissue ;
the former passing gradually into the latter, as



Fig. 319. j^




Enderon of the Skate.

we trace it inwards, developing its elastic ele-
ment to a greater or less extent, and acquiring
a more or less distinctly fascicular arrangement
of its collagenous element. In the higher
Vertebrata, these bundles are usually disposed
as an irregularly felted mass ; but in Fishes
and Batrachia, they form regularly super-
imposed horizontal strata, tied together by
perpendicular columns, which penetrate the
interspaces of the bundles, and spread out
into the irregular connective tissue on the
deep and superficial surfaces of the stratified
mass (fig. 319. A). On the addition of acetic
acid, it is seen that the boundaries of the strata
are formed by irregular bands of elastic tissue,
in which the remains of the primitive endo-
plasts may be seen (as in fibro-cartilage),
whose strongest fibres are horizontal, though
they send out others irregularly in all direc-
tions. The perpendicular columns are likewise
composed of bundles of pale elastic fibres (fig.
319.B), and if the intersection of the horizontal
with the vertical divisions be carefully examined,
it is seen that the former are, as it were, given
off by the latter, which thus gradually break
up and thin out, terminating above and below
in the elastic fibres of the unstratified super-
ficial and deep layers. A horizontal section of
this portion of the enderon presents a very
peculiar appearance, the transparent vertical
columns looking like radiating spaces, as which
they were, in fact, at first described.

Pigment of the enderon. The enderon
presents scattered masses of pigment, some-
times contained in cells and sometimes free,
in many Invertebrata (Annelids, Trematoda,
Echinoderms, Crustacea, Mollusca). In
other Invertebrata and in the higher Verte-
brata, the pigment is confined to the ecderon.
In Fishes and Reptiles, however, a well-
marked layer of pigment lies at the surface of
the enderon in the form of scattered granules



TEGUMENTARY ORGANS.



503



and of irregular more or less stellate masses
which are not enclosed in cells. The silvery
lustre of the skin of fishes is due to minute
rods which constitute a layer at this surface,
and should probably be regarded as a peculiar
form of pigment granules.

In the Cephalopoda and some Gasteropoda
among the Invertebrata, the integument
undergoes during life the most extraordinary
variations of colour, becoming overspread
with successive clouds of the most vivid hues.
These are produced by the contraction and
expansion of peculiar sacs the chromato-
phora containing masses of pigment granules.
According to H. Mutter, (whose observations
I have recently had the opportunity of re-
peating,) these are sacs attached to whose
walls are contractile fibre cells arranged ra-
dially, and frequently anastomosing with those
of other cells. They do not always contain
pigment, but frequently present a distinct nu-
cleus. Several layers of these chromatophora
of different colours are frequently disposed,
one over the other, in a given portion of the
skin, and produce by their different states of
contraction, relatively to one another, suc-
cessive changes in the colour of the spot.

Among the Vertebrata the Chameleon, as
is well known, presents similar phenomena.

Papilla of the enderon. The enderon is
frequently produced into conical or cylin-
drical processes, which either merely contain
a vascular loop, or are supplied, in addition,
with special nerves. In the Invertebrata, we
find, in the processes of the mantle into the
shell of the Brachiopoda described by Dr.
Carpenter, organs which, I have no doubt,
must be regarded, like the corresponding pro-
cesses in the Ascidians, as vascular papillae.
Among the Articulata like processes extend, in
the Crustacea, through the whole thickness of
the integument to its surface, giving rise to the
colourless spots observable on the shell of the
crab, for instance. I imagine, however, that
these spots were usually occupied by a hair
when the shell was thin. In the Mollusca,
the marginal processes of the mantle of the
Lamellibranchs and Gasteropods, the papillae
of Onchidium, &c. and those of Tremoctopus
(H. Muller) are very probably both vascular
and nervous papillae like those of fishes.

Among the Vertebrata, fishes present large
projecting papilke, particularly about the region
of the lips and operculum, which are both vas-
cular and nervous. Simple papillae (nervous?)
are scattered over the surface of the body in
Plagiostomes and some Ganoid fishes.

I am not aware that papillae have hitherto
been observed on the integument of Birds
and Reptiles. In most Mammals, they are very
small, if they exist at all, upon the general sur-
face of the body, attaining a considerable size
only in such organs as the ball of the foot
(Cat, Dog), or on the muzzle. The Cetacea,
however, appear to make a remarkable excep-
tion to this rule ; it is stated (Heusinger,
Breschet, and Roussel de Vauzeme) that the
very thick integument of these animals is tra-



versed by vascular and nervous papillae, four
or five lines long, which extend as far as the
outer horizontal horny layer of the ecderon,
so that a horizontal section of the ecderon is
like that of a horse's hoof. In man, again, the
papillae are, as is well known, so abundant as to
have given rise to the term pars papUlaris, for
the superficial layer of the ecderon. The
structure of those which appear to possess
special nervous functions will be considered
below.

Sensory appendages of the enderon. Very
little is known of the ultimate distribution of
the nerves to the integument in the Inverte-
brata, but we are indebted to Ley dig for
showing that in certain Crustacea, Insecta, and
Mollusca, it is very similar to what occurs in
the vertebrate classes. Thus in Argulus
fotiaceus the peripheral nerves become pale, and
divide, and at the point of division there is a
* nucleus ' as in the embryonic fibres of the
frog. In Artemia salina, Branchipus stagnalis,
and in the Heteropod Mollusk Carinaria, the
termination of the tegumentary nerves is es-
sentially similar. The larva of the Dipterous
insect Corethra, presents even peculiar sensory
appendages, in the delicate plumed hairs
which beset the sides of the body. These
are articulated in the ordinary way, and have
an internal ligament, a sort of spring, attached
to their base, which is enlarged and receives
the enlarged and cellaeform termination of a
nervous twig. It will be obvious that this
arrangement is peculiarly fitted for commu-
nicating the slightest vibration to the nerves.

In the Vertebrata (fishes, reptiles, man),
the ordinary mode of termination of the
integumentary nerves is in one or two
plexuses, whence the fine terminal branches
proceed, and end by dividing into minute
branches indistinguishable from the imperfect
elastic fibrils of the enderonic tissue. Loops
have also been observed, but it is impossible
to say whether, in any case, these are real ter-
minations or not. Gerber and Kolliker have
also described " nerve coils" in animals, and
in the conjunctiva and lips of man.

The simplest form of sensory appendage
in the Vertebrata is presented by the large
papillae of fishes, into which a bundle of nerve
fibres enters, some of which terminate in the
papillae, while others, whose looped bands may
be readily distinguished, probably pass out
again.

In certain fresh-water fishes (Barbus, Leu-
ciscus), Leydig has described papillae of this
kind, which have a cup-shaped depression at
their extremities, lodging a globular mass of
what he describes as modified epithelium.

Special modifications of the tissue of the
papillae for sensory purposes in the fingers,
tongue, lips, &c. of man have lately been dis-
covered by Meissner and Wagner, and de-
scribed by them, under the denomination of the
Corpuscula tactus. Kolliker, who doubts their
special relation to the tactile function, on the
other hand, prefers to call these bodies, axile
corpuscles. They are simply ovoid masses of im-

K K 4



504



TEGUMENTARY ORGANS.



perfect connective tissue occupying the centre

of the papillae, and further distinguished by

having their endoplasts and imperfect elastic

Fig. 320.




A papilla with its Corpusculum tactus surrounded by
three vascular papillae.

fibrils arranged transversely to the axis of the
papilla, so that they appear to be made up of
transverse superimposed laminae (fig. 320.).