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Parietal eye-pineal morphology in lizards and its physiological implications.

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Parietal Eye-Pineal Morphology in Lizards and Its
Physiological lmpl ications
G. CRAIG GUNDY AND GLORIA Z. WURST
DepartrneRt of Z o o l o g y and Enton2cilogy, Colorado State University,
Fort Collins. Colorado 80523
ABSTRACT
Pineal complexes in 85 species of lizards examined comprised
seven morphological types. Members of the same family do not necessarily have
the same pineal complex type. “Regressive” parietal eyes were not common except in certain arboreal lizards, primarily from the family Chameleontidae. The
parietal eye is often retained in burrowing lizards, presumably because these animals are occasionally exposed to light and the parietal eye is a more suitable
photoreceptor for a burrower than are lateral eyes. The pineal of certain lizards
possesses a finger-like projection that extends toward the parietal eye. This extension, along with pineal wall convolutions, results in more photoreceptor cells
oriented for maximal absorption of light. It is rare to find convolutions and an
extension in the same pineal. Cartilage deposits and blood sinuses may modify
the intensity and wavelength of light reaching the pineal. These observations
suggest that the intracranial pineal of lizards is a more important photoreceptor
than was previously realized, a situation that may be a factor in the occasional
“failure” of parietalectomy experiments
Approximately 60% of all lizard genera
include animals with three eyes (Gundy
and Wurst, ’76). In addition to the large
lateral eyes, they possess a small “third
eye” or “parietal eye” on top of their heads.
Research on this eye dates from 1829 when
Brandt and Ratzeburg, Dug& (1829) and
Edwards (1829) noted a round, differentially-pigmented area on the interparietal
scale of several species of Lacerta. Brandt
and Ratzeburg referred to it as a “special
glandular spot” on a median head scale.
Dug& and Edwards included parietal eye
spots in their figures but made no suggestion about their function. Subsequent
major publications by Bkraneck (1892),
Klinckowstrom (1893), Leydig (1890),
Nowikoff ( ’ l o ) , Ritter (1891), Schmidt
(’09 j , Spencer (1886), Studnicka (’05 j
and Warren (’11) described the morphology of the parietal eye and of its close embryological relative, the intracranial pineal
body. The parietal eye was found to have
a cornea, lens, retina and, possibly, a
nerve, but whether or not i t could actually
perceive light was not convincingly demonstrated for over half a century.
Initial support for a photoreceptive function came from ultrastructural investigaANAT. REC., 1 8 5 : 4 1 9 4 3 2 .
tions of the parietal eye retina (see Eakin,
’73, for review). It contains photoreceptor
cells remarkably similar to those found in
typical vertebrate lateral eyes. Photoreceptor cell processes synapse with ganglion
cells, and ganglion cell axons form a parietal nerve. Electrophysiological evidence
that this system does respond to light has
left little doubt that the parietal eye is a
functional photoreceptor ( o p . cit.). We
have hypothesized that this photic information allows lizards to synchronize activity with the variable climatic conditions
at high latitudes, and, thus, facilitates
success there (Gundy et al., ’75).
The intracranial pineal body is often referred to as the “epiphysis cerebri”, “pineal
gland”, or the “pineal”. Its ultrastructural
features have been described in a total of
seven lizard genera by Collin (’69), Lierse
(’65), Oksche and Kirschstein (’68), Petit
(’691, and Steyn (’60). A relatively small
number of photoreceptor cells is present,
many of which are degenerate. The lizard
pineal can, however, produce electrophysiReceived Dec. 12, ’75. Accepted Mar. 15, ’76.
1 Present address: Department of Zoology, University of California, Berkeley, California 94720.
2 Present address: Museum of Vertebrate Zoology,
University of California, Berkeley, California 94720.
419
420
G. CRAIG GUNDY AND GLORIA Z. WURST
ological responses to light (Hamasaki and
Dodt, ’69). Further studies by Collin and
Meiniel (’73a,b), Meiniel et al. (’75), and
Wartenberg and Baumgarten (’69) have
shown that the degenerate photoreceptor
cells are sites for metabolism and storage
of pineal indoleamines, especially serotonin.
The lizard pineal body has a homologue
in nearly all vertebrate brains, but parietal
eye homologues are present only in lampreys (termed a parapineal or a parietal
organ), in frogs (termed a frontal organ
or Stirnorgan), and in the Tuatara, a
lizard-like reptile surviving only in New
Zealand. In all cases the embryological
ongin of these structures is the roof of the
diencephalic region of the brain.
Despite the recent ultrastructural and
electrophysiological advances noted above,
our knowledge about overall comparative
morphology in a wide variety of parietal
eye-pineal systems has not increased appreciably since the original work of 18861911. The objective of this study is to determine whether different species of lizards
have different morphological types of parietal eye-pineal complexes and, if so, to
analyze the physiological and adaptive significance of the different forms.
MATERIALS AND METHODS
Lizards were collected by the first author
and Charles L. Ralph in the southwestern US. and by Bruce Firth i n Australia.
Others were purchased from dealers Ray
Singleton in Florida and East Bay Vivarium
in Oakland, California. Robert C. Stebbins
and Richard M. Eakin at the University
of California, Berkeley, made microscope
slides of sagittal sections of lizard heads
available to us.
Live specimens were killed by decapitation and the heads were immersed in 10%
unbuffered formalin at 21 “C for two weeks.
Heads were decalcified overnight in Decal
(unspecified chelating agents in dilute HC1
from Scientific Products, Evanston, Illinois). Tissues were trimmed and washed
in running tap water for 8-10 hours. Dehydration was effected by sequential onehour immersions in ethanol solutions of
6 0 % , 8 0 % , 95% and loo%, followed by
a two-hour clearing in xylene and a threehour infiltration in moIten paraffin (Tissue-
mat, m.p. 56.5”C, Fisher Scientific, Pittsburgh, Pennsylvania). After embedding, a
series of 15 pm sagittal sections was cut
from each tissue block. Cross-sections were
also prepared in some instances. Sections
were stained with toluidine blue 0, hematoxylin and eosin, Mallory’s triple stain
(Gray, ’54; p. 360, formula 13.41) or
Patay’s triple stain (Gray, ’54; p. 339,
formula 12.32). Semi-diagrammatic line
drawings were prepared using a Wild M-11
microscope and drawing tube. When the
plane of sectioning was not sagittal, adjacent sections were superimposed to complete the drawing.
RESULTS
Pineal complex morphological types
Pineal complexes in the 85 lizard species
examined comprised several morphological
types. These types are determined by the
form of the parietal eye, the parietal foramen and the pineal body (figs. 1-7). A
“well-developed parietal eye has a distinct
lens and retina; a “regressed’ parietal eye
does not. The parietal foramen is noted as
absent if there is no trace of i t or if it is
covered by a thin bone. Possible reduction
of foramen size in older animals did not
appear significant. The pineal body is categorized on the basis of relative size and/or
wall thickness. For example, the difference
between types I and 111 is that type I has
a typical thin-walled, prominent pineal,
whereas type I11 has an atypically small,
thick-walled pineal (see insert to fig. 3).
Morphological variables
Morphological variables not affecting
the assignment of pineal complex types
are degree of pineal wall convolution and
the occurrence of a finger-like extension
from the pineal body projecting craniad
along the midline (figs. 8,9). Convolutions
are noted as absent, few, many and lateral.
Lateral convolutions are those which appear as separate pineal vesicles when the
section is not cut exactly in the midline.
Pineal extensions may be absent, short, of
intermediate length or long enough to
reach the parietal eye.
Pineal complex associated structures
Cartilaginous deposits and blood sinuses
occur near the pineal body of certain
PARIETAL EYE-PINEAL MORPHOLOGY IN LIZARDS
lizards (table 1). These structures do not
affect the assignment of morphological
types. Cartilaginous deposits are depicted
in figures 1-3, 6 and 7, and a blood sinus
is depicted in figure 8. The reliability of a
blood sinus “absent” entry is not good
owing to the possibility that a blood sinus
may collapse during histological processing, thus becoming invisible.
DISCUSSION
Pineal complex morphological types
Members of the same family showed
some tendency to have the same pineal
complex type, but there were many exceptions. This is surprising since all members
of the same family tend to be alike with
regard to the possession of a parietal eye
(Gundy and Wurst, ’76). The absence of
a discernible relationship between pineal
complex types and phylogenetic affinities
may be due to insufficient sample size.
Also, if such a relationship exists, it may
be obscured because the types into which
pineal complexes were classified represent
a n arbitrary grouping necessary for the
presentation of a large number of morphological characters. The problem of adaptive
significance can be investigated more easily
by looking at the morphology of specific
pineal complex structures.
Parietal eye morphology
In lizards possessing a parietal eye, the
lens and retina are usually well-developed.
A notable exception involves certain species (Chameleo gracilis,Chameleo p u r d a h ,
Chameleo vulgaris) from the family Chameleontidae, whose parietal eyes appear as
hollow vesicles with no apparent differentiation. In some cases this regressed
“eye” remains connected to the distal end
of the pineal body, presumably reflecting
its embryological origin (see DISCUSSION
i n Pineal morphology section). In Chameleo vulgaris the vesicle lies near the distal
edge of the foramen (fig. 4), reminiscent
of the completely extra-cranial location of
the frog’s frontal organ. A further similarity between these homologues (parietal
eye, frontal organ) is that, at the light microscope level, both lack the well-defined
lens, lumen, and retina found i n most parietal eyes. Ultrastructural and electrophys-
421
iological investigations of the frog’s frontal
organ have revealed functional photoreceptor cells (see Eakin, ’73, for review), but
such studies have not been carried out
on a lizard possessing a regressed parietal
vesicle.
All genera in the arboreal family Chameleontidae have parietal eyes in at least
one species, but many other species have
none (Gundy and Wurst, ’76). This high
degree of variability was not observed in
any other family. Neither was there any
other lizard studied. except the arboreal
agamid Draco, whose parietal eye resembled the undifferentiated vesicles present
in chameleons. These data suggest that
arboreal living, combined with other factors outlined below, may influence parietal
eye regression. Further support comes from
the fact that the sole parietal-eyeless genus
in the family Iguanidae (Uracentron) is
arboreal. Of the five parietal-eyeless genera
in the family Agamidae, the natural history
of three is known. Two (Cophotis and
Harpesaurus) are arboreal; the third
(Leiolepis) is a ground dweller. Of the
three parietal-eyeless genera in the family
Scincidae, the natural history of two is
known. One (Corucia) is arboreal; the
other (Voltzhowia) is a burrower. Of the
two parietal-eyeless genera in the family
Lacertidae, the natural history of one
( H o l a s p i s ) is known, and it is arboreal
(Gundy, ’74). Corucia and Holaspis are
significant because arboreal modifications
are rare among skinks and lacertids. Since
the absence of a parietal eye is also unusual in these two families, the coincidence of parietal-eyelessness and arboreal
lifestyle suggests that they may be related.
Additional factors that appear to be related to parietal eye regression are reduction of seasonal light and climatic fluctuation, reduced seasonality in breeding
habits, reduced stresses of thermoregulation and desiccation and, perhaps, reduced
exposure of the parietal eye to the zenith.
This last situation occurs in arboreal lizards that spend most of their time on
trunks of trees with head directed upward,
an orientation that points the optical axis
of the parietal eye in a horizontal direction. Behavioral studies of parietal-eyeless
arboreal lizards are needed to test this idea.
Gundy (’72, ’74) noted that the parietal
422
G. CRAIG GUNDY AND GLORIA 2. WURST
TABLE 1
Morphology of t h e parietal eye-pineal complex in lizards
Morphologiical
variables
Morphological
tvve
1(?)
I (pineal? )
I (pineal?)
I
I
I
I
I (pineal?)
I
I (pineal?)
I (pineal? )
I
I
I
I
I
I
I (pineal?)
I
I
I
I
I
I
I
1(?)
I
I (pineal? )
I
I
I
I (pineal?)
I
I (pineal? )
I
I
I
I
I
I
I
I
I
I (pineal? )
I
I
I
I
I (pineal?)
I1
I1 (pineal? )
I1
Species
(f amilv
Calotes cristatellus (Ag)* emb
Calotes ophiomaca (Ag)3
Moloch horridus (Ag)3
Anguis fragilis ( A r ~ g ) ~
Gerrhonotus hingii (Ang)
Gerrhonotus multicarinutus ( Ang)
Ophisaurus apodus (Ang)*
Amblyrhynchus cristatus (Ig)
Anolis carolinensis ( I g )
Callisaurus draconoides (Ig)
Callisaurus ventralis ( I g ) x-s
Crotaphytus collaris ( I g )
Dipsosaurus dorsalis (Ig)
Iguana iguana (Ig)
Oplurus sebae (Ig)z
Phrynosoma coronatum (Ig)
Phrynosoma douglassi (Ig)
Plica umbra (Ig)3
Sceloporus poinsetii (Ig)
Sceloporus undulatus ( I g )
Tropidurus albemarlensis (Ig)
Uma inornata (Ig)
Urosaurus ornatus ( I g )
U t a graciosa (Ig) x - s
U t a nearnsi (Ig)
Uta stnnsburiena (Ig) x-s
Lacerta agilis (Lac)5
Lucerta galloti (Lac)2
Lacerta muralis (Lac)6
Lacerta ocellata (Lac)S
Lacerta viridis (Lac)5*6
Lacerta uivipara (Lac)' emb
Chalcides chalcides ( S C ) ~
Chalcides tridactylus ( S C ) ~ , ~
Eumeces fasciatus ( S c )
Eumeces gilberti ( S c )
Eumeces obsoletus (Sc)*
Eumeces schneideri ( S C ) ~
Eumeces shiltonianus ( S c )
Leiolopisma laterale ( S C ) ~
Mabuyaelegans (Sc)*
Mabuya multifasciata ( S c )
Mahuya quinquetaeniata ( S c )
Scincus ogcinalis ( S C ) ~
Siaphos equalis (Sc)
Siaphos lentiginosus (Sc)
Tiliqua gigas ( S C )emb
~
Varanus bengalensis (Va)3
Vuranus giganteus (Va)s
Cordylus jonesii ( C o )
Gerrhosaurus nigrolineatus ( C O ) ~
Acontias percivali ( S C ) ~
'
Pineal wall
convolutions
Fineal
extensions
absent
few, lateral
?
absent
absent
absent
many, lateral
long
intermediate
long
long
long
long
long
?
short
absent
?
intermediate
intermediate
absent
intermediate
short
absent
long?
intermediate
short
short
short
short
?
absent
few
few?
few
absent
many
few
absent?
few
few?, lateral?
few, lateral
many
few
absent
absent
few
absent
few
absent
many
absent
few
absent
absent
absent
absent
many, lateral
absent
absent
absent
absent
absent
absent
absent?
few
?
absent
absent
absent
many?, lateral
many?, lateral
absent
?
absent
?
short
?
long
absent
absent?
intermediate
long
absent
short
absent?
long
short
long
long
short
long
long
long
long
long?
short
absent
intermediate
long
long
absent
?
absent
Associated structures
Cartilage Blood sinus
over pineal near pineal
?
absent
absent?
absent
absent
?
absent
absent
present
absent
present
absent
?
?
present
present
absent?
ahsent
present
present
absent?
present
absent
?
absent?
present
?
present
present
absent?
absent
present
?
absent
present
present
present
present
absent
absent?
present
absent
?
present
absent
?
absent
absent
absent
present
absent ?
absent
absent
present
absent?
present
?
absent
present
absent
present
present
absent
present
present
absent
present?
present
?
absent
absent
?
absent
absent
absent
absent?
absent
?
present
absent
present
present
present
present
present
absent
absent
present
present
?
present
present
?
absent
?
present
?
present
?
absent
?
absent
present?
absent
423
PARIETAL EYE-PINEAL MORPHOLOGY I N LIZARDS
TABLE 1 (continued)
Morphological variables
Morphological
type
I1
I11
I11 (pineal? )
I11 (pineal?)
I11 (pineal? )
I11
111 (pineal? )
I11
IV
I V (pineal?)
IV
IV
V
V
V
V (pineal?)
VI
VI
VI (pineal?)
VI
VI
VI
VI
VI (pineal?)
VI
VI
VI
VI
VI
VI
VI
VII
VII (pineal? )
Species
(family)
Pineal wall
convolutions
Riopa sundevalli ( S C ) ~
absent
AnoEis sngrei ( I g )
absent
Sceloporus graciosus ( I g )
few
Sceloporus occidentalis ( I g )
many
Sceloporus orcutti (Ig)
few
Hemiergis decresiense ( S c )
absent
Xantusia henshawi (Xa)
absent
Xantusia vigilis (Xa)
absent
Draco volans (Ag)
absent
Chameleo grncilis ( Ch)z
?
Chameleo pardalis ( Ch)2
absent?
Chameleo vulgaris (Ch)3
few
Hemidactylus brooki ( G e )
few
Hemidactylus flauiviridis ( G e )
few
Hemidactylus turcicus ( G e )
absent
Voltzkowia mira ( S C ) ~
absent
Chameleo jacksonii (Ch)
absent
Zonosaurus madagascariensis ( C O ) ~ absent
Coleonyx variegatus (Ge)
few
Gehyra oceanica (Ge)'O emb
absent
Pkelsuma madagascariense ( Ge)2
many
Phyllodactylus tuberculosus ( G e )
absent
Tarentola annularis ( G e ) 2
absent
Tarentola muralis ( G e ) 4
absent
Ameiva ameiua (Te)
many, lateral
Cnemidophorus lemniscatus (Te)
many, lateral
Cnemidophorus sachi (Te)
many, lateral
Cnemidophorus sexlineatus (Te)
many, lateral
Cnemidophorus tigris ( T e )
many, lateral
Cnemidophorus velox ( T e )
few, lateral
Tupinambis teguixin (Te)
few
Anniella pulchra ( A n n )
absent
Feylinia currori ( S C ) *
absent?
Pineal
extensions
long
absent
absent
absent
short
short
absent
absent
short
long
intermediate
long
absent
absent
absent
absent
long
absent
absent
short
absent
absent
short
absent
absent
absent
absent
absent
absent
absent
intermediate
absent
absent?
Associated structures
Cartilage Blood sinus
over pineal near pineal
present
present
present
present
present
present
present
absent
present
?
?
absent
absent
absent
absent
absent?
present
absent?
absent
?
absent
absent
absent
absent
present
present
absent
present
present
present
present
present
absent
absent
absent
absent
present
present
absent
present
present
present
?
?
absent
absent
present
present
present
absent
absent
present
?
present?
absent
present?
absent
present
absent
present
present
absent
absent
absent
absent
absent
1 Within each moroholoeical tvDe. families are listed alohabeticallv: within each family, genera are listed
alphabetically. Question marks inhicite that-thi- CGiGiS ,f questionable reliability, or that information is not
available. Abbreviations: Ag Agamidae. Ang Anguidae, Ann, Anniellidae; Ch, Chameleontidae; Co, Cordylidae;
emb. embrvo; Ge. Gekkonidae: Is. IeuHnidak: Lac. Ladertidae;. Sc,, Scincidae; Te, Teiidae; Va, Varanidae; Xa,
Xantusiidae; .x-s,'cross section, all orhers are' sagittal.
ZFrom Schmidt, '09. Schmidt frequently includes what appears to be a blood sinus but does not label i t '
3 From Spencer, ' 86. Presence of blood sinus in Angvis f ~ n g i l i sfide
,
Petit, '69.
4 From Studnicka, '05.
5 From Leydig, '90.
6 From Swain, '68.
7 From Francotte, '96.
8 From Gundy, '72.
9 From Prenant, '96.
10 From Stemmler, '00.
eye of the burrowing lizard Feylinia currori appears to be degenerate and that the
parietal eye is totally absent in the burrowers Voltzhowia mira and Anelytropsis
papillosus. Since these forms show extreme
specialization to a subterranean habitat,
including regression of the lateral eyes,
parietal eye reduction was expected. However, the parietal eye of most other burrowers is retained. This situation may exist
because the parietal eye is more suitable
to a burrowing lifestyle than are latera1
eyes. Since Schmidt ('19) reported that
one Feylinia currori was caught in the
424
G. CRAIG GUNDY A N D GLORIA 2. WURST
grass at noon, we must assume that even
highly specialized burrowers occasionally
expose themselves to intense light. Furthermore, some of these animals undertake
diel vertical migrations and “bask” just
under the surface where a considerable
amount of light and heat does penetrate.
Therefore, they could use a light detector
to phase and/or monitor such movements.
A role in diel phasing of activity cycles
(Palenschat, ’64) and a role in annual
phasing of reproductive and thyroid cycles
(Stebbins and Cohen, ’73) have been demonstrated for the parietal eye. Lateral eyes,
specialized for epigean sight, are neither
necessary nor suitable for such functions
in burrowing animals which rely primarily
upon olfaction and tactile sensing. Imageforming capability requires complex focusing and aiming musculature, elaborate
nerve connections, tear ducts, moist membranes and a relatively large criticallyshaped cornea and lens. Many of these
structures would be severely damaged by
the pressure, sharp objects and abrasion
encountered during burrowing. The ensuing risk of infection would reduce the animal’s fitness and this could be an important factor i n the reduction of lateral eyes
in subterranean lizards. The parietal eye,
however, is suitable for a burrower. It does
not possess tear ducts, moist membranes
and a relatively large critically-shaped dioptric apparatus. It is smaller than lateral eyes and i t is protected by tough scales
or by a thin bone covering the parietal
for amen,
Pineal morphology
A finger-like extension projects craniad
from the pineal in approximately 48 of 85
species studied. This extension is similar
to a developmental anomaly described by
Eakin (’64) in Sceloporus occidentalis.
Normally, the presumptive parietal eye
buds off the left side of the pineal evagination and migrates to its final position over
the cerebrum. The eye separates completely
and has no effect on the shape of the
pineal body. In two specimens, however,
it failed to separate and in one it pulled
a pineal extension along. This process may
play a role in normal development of pineal extensions - of the 31 lizards with
either a long or intermediate extension, all
possess parietal eyes except Chameleo
jacksonii and Tupinambis teguixin.
Pineal extensions showed a peculiar relationship with degree of convolution of
the pineal body. Pineals of 14 species had
many convolutions; pineals of 31 species
had prominent extensions, but only four
species had both. As pointed out above, an
extension is most likely to occur when a
parietal eye is present. If a parietal eye is
not present an extension is rarely found,
but pineal convolutions seem to take its
place and may serve a similar function.
This function may be to optimize photoreceptor cell orientation. When the long
axis of a photoreceptor cell is parallel to
the direction of incoming light, the outer
segment discs lie perpendicular to the optical axis. This appears to permit maximal
absorption of radiant energy (Eakin, ’73).
Since Hamasaki and Dodt (’69) found that
the amount of light reaching the pineals
of the lizards Iguana iguana, Acanthodactylus erythricrus and Lacerta sicula is
sufficient to elicit a n electrophysiological
response only in bright day-light, any modification to increase its sensitivity would be
important. Pineal convolutions and extensions may be such modifications. Pineal
convolutions would put additional pineal
photoreceptors in the appropriate orientation with respect to incoming light and
would result in more photoreceptors per
pineal than would a non-convoluted pineal
of the same size. Pineal extensions should
also result in additional photoreceptors
oriented for maximal absorption of light.
Ultrastructural studies are underway to
check this prediction.
Pineal complex associated structures
Cartilaginous deposits occur in the skull
over the pineal in 37 of 85 species studied.
The pattern of occurrence bears no detectable relationship with other morphological
parameters described here. Considering
the high threshold of lizard pineal photoreceptive capability (Hamasaki and Dodt,
’69), it is likely that these deposits are important “windows” facilitating penetration
of light.
A median longitudinal blood sinus occurs
over the pineal region of most lizards (see
Steyn, ’58 and Swain, ’68), but reliable
visualization was not possible with speci-
PARIETAL EYE-PINEAL MORPHOLOGY IN LIZARDS
425
l’organe pineal. De l’epiphyse sensorielle a l a
mens available for this study. Swain (’68)
glande pinbale: Modalites de transformation et
suggested that the pineal vascular system
implications fonctionelles. Annls. Stn. Biol.
would provide an efficient means for transBesse-en-Chandesse, Suppl. I, 1-359.
portation of secretory products to and from Collin, J. P., and A. Meiniel 1973a Metabolisme
the pineal complex. Also, Hamasaki and
des indolamines dans l’organe pineal de Lacerta
(Reptiles, Lacertiliens) I. Intggration selective
Dodt (’69) found that this blood sinus filde 5-HTP-3H (5-hydro~ytryptophane-~H) et
ters light to the pineal and transforms its
retention de ses dkrives dans les photorecepteurs
trimodal response curve into a smooth unirudimentaires secretoires. 2. Zellforsch., 142:
modal curve. The pineal exhibits a high
549-570.
1973b Metabolisme des indolamines
rate of spontaneous activity which is indans l’organe pinkal de Lacerta (Reptiles,
hibited by light. More light causes more
Lacertiliens ) 11. L’activite MA0 et l’incorporainhibition. If the degree of dilation of this
tion de 5-HTPJH et de 5-HT-3H, dans les consinus is variable, as it undoubtedly is, then
ditions normales et experimentales, 2. Zellforsch., 145: 331-361.
the sinus could regulate the intensity and
A. 1829 Memoire sur les espbces indiwavelength of light reaching the pineal, Duges,
genes du genre Lacerta. Ann. Sci. Nat., 16:
thereby changing its electrophysiological
337-389.
output.
Eakin, R. M. 1964 Development of the third
eye i n the lizard Sceloporus occidentalis. Rev.
These elaborate modifications suggest
Suisse Zool., 7 1 : 267-285.
that the pineal may play a n important role 1973 The Third Eye. University of
in the photoreceptive capability of the paCalifornia Press, Berkeley, California, pp. 106rietal eye-pineal system. This should be
137.
considered i n experimental designs utiliz- Edwards, H. M. 1829 Recherches zoologiques
pour servir a l’histoire des lezards extraites
ing parietal eye ablation or shielding. Phod‘une monographie de ce genre. Ann. Sci. Nat.,
toreception by the intracranial pineal may
16: 50-89.
be responsible for the occasional equivocal Engbretson, G., and C. M. Lent 1976 Parietal
eye of the lizard: Neuronal photoresponses and
results and “failures” of experiments that
feedback from the pineal gland. Proc. Nat.
deal solely with the parietal eye. To test
Acad. Sci., 73: 654-657.
these speculations, traditional parietal eye Francotte,
P. 1896 Contribution B l’etude de
behavioral experiments should be repeated
l’oeil parietal de l’epiphyse et de la paraphyse
chez les Lacertilia. Acad. R. Belg. Mem. Cour.,
with a n additional experimental group in
55: 1-45.
which the pineal area is covered by a n
P. 1954 The Microtomist’s Formulary and
opaque shield. Our data further suggest Gray,
Guide. Blakiston, New York, pp, 339 and 360.
that interactions between the parietal eye Gundy, G. C. 1972 A comparative morphologiand intracranial pineal should occur. Indical study of the epiphyseal complex in skinks.
M. S. Thesis, University of Pittsburgh.
cations of such a n interaction have been
1974 The evolutionary history and
obtained by Engbretson and Lent (’76).
comparative morphology of the pineal complex
ACKNOWLEDGMENTS
This work was supported in part by NIH
grant NS08554 to Charles L. Ralph and
NSF grant G-333070 to Robert C. Stebbins
and Richard M. Eakin. Parts of these data
were taken from a dissertation submitted
by the first author to the University of
Pittsburgh. We thank Richard M. Eakin,
Clarence J. McCoy, Robert C. Stebbins and
Philip J. Regal for offering suggestions on
the manuscript.
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PLATES
Paraphysis
Posterior cominissure
Parietal eye
Pineal
Subcommissural
organ
O F FIGURES
Type I1 parietal eye-pineal morphology, exemplified by Cordylus jonesii. The parietal eye is well-developed, the parietal foramen is absent and the pineal is thinwalled and large. In addition, note the cartilaginous deposit in the cranium over
the pineal.
Type I11 parietal eye-pineal morphology, exemplified by Hemiergis decresiense.
The parietal eye is well-developed, the parietal foramen is present and the pineal
is thick-walled or small. In addition, note the cartilaginous deposit in the cranium
near the pineal. Insert ( 3 a ) shows the pineal of another specimen.
Type IV parietal eye-pineal morphology, exemplified by Chanieleo vulqaris. The
parietal eye is regressed, the parietal foramen i s present and the pineal is thinwalled and large. From Spencer (1886).
2
3
4
parietal eye is well-developed, the parietal foramen is present and the pineal is
thin-walled and large. In addition, note the cartilaginous deposit in the cranium
over the pineal.
1 Type I parietal eye-pineal morphology, exemplified by A?zolis carolinensis. The
EXPLAh'ATION
PLATE 1
Anterior is to the left i n all figures. Bar indicates 1 mm.
pa,
pc,
pe,
pi,
so,
Abbreviations
ac, Aberrant commissure
bo, Bone of skull
bs, Blood sinus
cb, Cerebrum
ct; Cartilage
hc, Habenular commissure
w
>-
a
I-
429
w
ip
0
Type V parietal eye-pineal morphology, exemplified by Hemidactylus brooki. The
parietal eye is absent, the parietal foramen is absent and the pineal is thick-walled
or small.
Type VI parietal eye-pineal morphology, exemplified by Cnenzidophorus v e l o x .
The parietal eye is absent, the parietal foramen is absent and the pineal is thinwalled and large. In addition, note the cartilaginous deposit i n the cranium over
the pineal.
Type VII parietal eye-pineal morphology. This type includes species that do not
fit the common categories. I n Anniella pulchra, figured here, the parietal eye is
well-developed, the parietal foramen is absent and the pineal is small, thick-walled
and spherical. I n addition, note the cartilaginous deposit i n the cranium over
the pineal.
A n example of a highly convoluted pineal is shown here in the type VI pineal
complex of Cnemidophorus sacki. A blood sinus is also present.
An example of a long pineal extension is shown here i n the type I pineal complex
of Gerrhonotus hingii.
5
6
7
8
9
EXPLANATION O F FIGURES
PLATE 2
6
so
TYPE VI
TYPE V
PARIETAL EYE-PINEAL MORPHOLOGY I N LIZARDS
G. Craig Gundy and Gloria Z. Wurst
a
ac
9
TYPE VII
PLATE 2
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