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The skin of the whale (Balaenoptera physalus).

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The Skin of the Whale (Bcrlaenoptercr physalus) '
LUIGI GIACOMETTI
Oregon Regional Primate Research Center,
Beaverton, Oregon
ABSTRACT
Skin specimens were obtained from every representativc region of
the body of a n adult Finback whale (BaEaenoptera physalus) and examined by means
of various histochemical and histological techniques. The following characteristic
features were found:
The epidermis is exceedingly thick over the general body surfaces and varies from
a maximum of 3.0 mm over the ventral surface to 2.5 m m on the back.
The complex understructure of the epidermis has rete ridges oriented to the craniocaud,ad body axis.
The papillary layer of the dermis has long and pointed papillae which are wedged
into the epidermis.
The sensory cutaneous nerve endings demonstrated by silver impregnation and
cholinesterase consist predominantly of small Vater-Pacini corpuscles situated in the
higher level of the dermis.
The intricate blood capillary network, positive for alkaline phosphatase is encased
in the dermal papillae.
There are no hair follicles, sebaceous and sweat glands.
Japha in 1905 was the first to describe
the gross anatomy of the skin of the whale.
Biief observations on the histological characteristics of the fetal and adult skin, particularly its circulatory system, were made
by Parry ('49). However, n o one to our
knowledge has made a systematic study
of the entire skin. This paper presents our
observations on some histological and histochemical features of the skin of the Finback whale.
MATERIALS AND METHODS
technique ('50). To study the epidermal
understructure and the epidermal-dermal
relationship, pieces of skin were immersed
for about 30 minutes in a preheated aqueous solution of 2N NaBr at 37°C (Staricco
and Pinkus, '57); then the epidermis was
separated from the dermis with watehmaker's forceps under a dissecting microscope. The epidermal and dermal sheets
were fixed 24 hours in 10% formalin dehydrated, cleared, and attached to a glass
slide with a Scotch 6 double-coated tape
(no. 665).
Skin specimens for this study were obOBSERVATIONS
tained from every representative region of
a n adult female Finback whale (BalaGeneral descriptions
enoptera physaEus) , Alkaline phosphatase
The
external
features of the Finback
(Gomori, '52) and cholinesterases (techwhale
have
been
described by Grasse ('55)
nique of Koelle and Friedenwald, '49, as
modified by Gomori, ' 5 2 ) were demon- and Slijper ('62), and we have little to add.
strated in frozen sections, 50-60 p thick, Our specimen was 16 m long, 2.8 m wide,
of tissues fixed four hours in chilled, 10% and weighed approximately 47 metric tons.
neutral formalin. Cutaneous nerve endings The back was bluish-black and the underwere stained in frozen sections by means side yellowish-white. A series of longitudiof the silver impregnation method of nal furrows, about 35 in number and 2.0
Winkelmann and Schmit, ('57). Paraffin cm deep, were present on the throat and
sections of tissues fixed in 10% formalin chest regions. The nostrils opened exterwere stained with hematoxylin and eosin nally through a double blowhole located on
and Van Gieson's picrofuchsin for the dem1 Publication no. 268 from the Oreeon Reeional
Center, supported in part by -grant
onstration of dermal collagen (McManus Primate-Research
FRO0163 of the Natxonal Institutes of Health and by
and Mowry, '65). The elastic tissues were funds from grant A M 0 8 4 4 5 Biology of the Skin of
and Other Primates. Also supported by the
studied with Gomori's aldehyde fuchsin Man
Revlon Research Center, Inc., New York.
ANAT. REC.,159. 69-76
69
70
LUIGI GIACOMETTI
the highest point of the head. External
ears were absent, and the auditori meatus
consisted of a small opening about 5 m m
in diameter which ran in an S-shaped
fashion through the blubber to the e x drums. The eyes were comparatively small,
and thick eyelids without eyelashes covered
the cornified outer cornea.
T h e epidermis
The epidermis was very thick over the
general body surface and vaned from a
maximum of 3.0 mm over the ventral surface to 2.5mm on the back (fig. 1 ) . The
malpighian layer was not well defined and
the stratum corneum was practically absent except in the external genitalia and
the eyelids, which measured 100 p and 50 p
respectively. The underside of the epidermis was exceedingly elaborate; it had long
rete ridges which formed parallel wavy
cristae oriented to the craniocaudad body
axis (fig. 2).
The external surface of the epidermis
was carved by continuous small furrows
and plicae aligned in a definite pattern
along the body.
The epidermis, except on the belly, was
heavily pigmented and every cell was laden
with pigment granules. The melanocytes
were most numerous at the apices of the
epidermal ridges; there were a few in the
epidermis between the ridges.
The dermis
The structure of the dermis varied from
region to region. In the lips, eyelids, external genitalia, and blowhole, the reticular layer consisted of thick piles of horizontally distributed collagen fibers which
were alternately oriented in opposite directions; in the dorsal and ventral regions
coarse collagenous bundles imbedded in
areolas tissue formed a lax type of plexus.
The papillary layer was an intricate array
of long, pointed papillae which alternated
with short ones; figure 3 shows a split skin
preparation of such dermal papillae.
There were no elastic fibers in the papillary layer, but some could be found in the
lower level of the dermis, aligned parallel
to the surface.
The specialized sensory cutaneous end
organs in the whale consisted predominantly of small Vater-Pacini corpuscles, weakly
reactive for cholinesterase, housed in the
higher level of the dermis beneath the
dermal papillae. An example of a VaterPacini end organ is shown in figures 4-5.
The number of Vater-Pacini corpuscles
varied in different areas; they were scanty
in the back and the belly and numerous in
thc lips and eyelids. In the external genitalia, round masses of neurofibrils were
encased in the rete ridges and resembled
the Winkelmann mucocutaneous end organs (fig. 6 ) . In the lips and eyelids, oceasional small neurofibrils gave rise to fine
filaments which wandered inside the rcte
ridges; some of these terminated in slender
processes near, but neither inside nor in
contact with, the epidermis.
Since we studied the vascular system
only in preparations that were staincd for
alkaline phosphatase, blood vessels nonreactive for phosphatase may have escaped
observation. Despite this limitation, our
study showed the skin of the whale to be
abundantly vascularized. I a g e arteries
from the hypodermis formed a horizontal
large plexus in the middle dcrmis; from the
dermal plexus, single arterioles rose to the
upper dermis, branched out, and sent
triads of capillaries which arched and
twisted within the intricate dermal papillae.
The skin of the whale has no hair follicles and no sebaceous and sweat glands.
COMMENTS
The morphological peculiarities of the
skin of the whale reflect the adaptation
that it has had to make to an exclusively
aquatic existence. The epidermis has a
complex understructure of rete ridges
which ensures an intimate contact with
the dermis, which contact has a protective
function against the hydrodynamic friction of swimming. The conspicuous rete
ridges oriented to the craniocaudad body
axis cause small folds in the skin surface
which, in turn, may have an antiturbulent
function (Sokolow, '62). The epidermis of
the whale has some characteristics in common with that of other amphibious mammals; e.g., it is thicker on the ventral than
on the dorsal surface. This, of course, is
the reversal of the pattern in terrestrial
species.
THE SKIN O F THE WHALE (BALAENOPTERA PHYSALUS)
The dermis of the whale is distinctive
in having an extensive papillary layer over
a thin, flexible reticular layer. If the derm i s has lost something of its tautness, it
has gained in suppleness; and this would
seem to be an excellent adaptation since,
for a body that must remain agile in the
water, a thick, coriaceous dermis would be
an impediment rather than an asset.
In spite of topographic variations, the
papillary layer of the dermis is always
thick and riddled with a complex capillary
network.
LITERATURE CITED
Gomori, G. 1950 Aldehyde fuchsin: A new
stain for elastic tissue. Am. J. Clin. Path., 20:
655-666.
1952 Microscopic Histochemistry: Principle and Practicc. University of Chicago Press,
Chicago, Illinois.
Grass& P. P. 1955 Trait6 de Zoologie. Tome
XVII Mammifkres. Masson et C. &diteurs, Pans.
71
Japha, A. 1905 Ueber den Bau der Haut dei
Seihwalcs (Balaenoptera borealis Lesson). Zool.
Anzeiger., 29: 442-445.
Koelle, G. B., and J. S. Friedenwald 1949 A
histochemical method for localizing cholinesterase activity. Proc. Soc. Exp. Biol. Med., 70: 617622.
McManus, J. F. A., and R. W. Mowry 1960
Staining Methods: Histologic and Histochemical. Hoeber Medical Division, Harper and Row,
New York, New York, pp. 23G231.
Parry, D. A. 1949 The structure of whale blubber and a discussion of its thermal properties.
Quart. Journ. Micro. Sic., 90: 13-25.
Slijpcr, E. J. 1962 Whales. Hutchinson and
Company, London.
Sokolow, W. 1962 Adaptations of the mammalian skin to the aquatic mode of life. Nature,
195: 461-466.
Staricco, R. J., and P. Pinkus 1957 Quantitative and qualitative data on the pigment cells
of adult human epidermis. J. Invest. Derm., 28:
33.
Winkelmann, R. K., and R. W. Schmit 1957 A
simple silver method for nerve axoplasm. Staff
Mtg. Mayo Clin., 32: 217-222.
PLATE 1
EXPLANATION O F FIGURPS
72
1
Vertical section of skin from the back showing the thick, pigmented
epidermis. X 70.
2
Epidermal understructure of the ventral region. The epidermal projecting rete ridges are visible in the parallel wavy cristae; the
darker areas represent the recesses left by the dermal papillae. x 25.
3
Surface pattern of the dermis of the ventral region. Kote the long
and pointed dermal papillae. x 25.
THE SKIN OF THE WHALE (BALABKOPTERA PlfYSALUS)
Luiai Giacometti
PLATE 1
73
PLATE 2
EXPLANATION OF FIGURES
4
Vertical section of the skin from the back showing Vater-Pacini end
organs. Winkelmann’s silver impregnation method. x 375.
5
Sagittal section through the lip showing a Vater-Pacini end organ
beneath a dermal papillae. Winkelmann’s silver impregnation method.
x 375.
6
A round mass of neurofibrils (arrow) encased in the rete ridges of
the external genitaKa. Winkelmann’s silver impregnation method.
x 400.
74
THE SKIN OF THE WHALE ( B A L A E N O P T E R A P H Y S A L U S )
Luigi Giacometti
PLATE 2
75
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