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THE AMERICAN ANATOMICAL MEMOIRS

THE MORPHOLOGY AND EVOLUTIONAL
SIGNIFICANCE OF THE PINEAL BODY

BEING

PART I

OF

A CONTRIBUTION TO THE STUDY OF THE EPIPHYSIS

CEREBRI WITH AN INTERPRETATION OF THE

MORPHOLOGICAL, PHYSIOLOGICAL AND

CLINICAL EVIDENCE

FREDERICK TILNEY, M.D., PH.D.

PROFESSOR OF NEUROLOGY, COLUMBIA UNIVERSITY

AND

LUTHER F. WARREN, A.B., M.D.

PROFESSOR OF MEDICINE, LONG ISLAND COLLEGE HOSPITAL

1919

PUBLISHED BY
THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY

PHILADELPHIA

,•:.

re

V

CONTENTS OF PART I

•

1. Introduction 5

2. Nomenclature 7

3. General review of the literature 9

4. The comparative morphology of the pineal region 17

1. In cyclostomes 21

2. In selachians 23

3. In ganoids 25

4. In teleosts 27

5. In dipnoi 29

6. In amphib'a 30

7. In reptilia 31

8. In aves 36

9. In mammals 37

5. The comparative embryology of the epiphyseal complex 39

1 . In cyclostomes 39

2. In selachians 41

3. In ganoids 48

4. In teleosts 50

5. In amphibia 53

6. In reptilia 56

7. In aves 67

8. In mammals 72

6. The comparative anatomy and histology of the epiphyseal complex 80

1 . In cyclostomes 80

2. In selachians 92

3. In ganoids 98

4. In teleosts 103

5. In amphibia 114

6. In reptilia 119

7. In aves 148

8. In mammals 155

7. Discussion • 196

1. Significance of the pineal region 196

2. Evidence based on the gross morphology of the epiphyseal complex — 203

a. Phyletic constancy 203

b. Phyletic variation and morphologic specialization 205

c. Relative constancy of the epiphyseal complex with reference to

other structures of the pineal region 211

d. Relative constancy of the epiphyseal complex with predomi-

nance of the proximal portion 211

3

4 CONTENTS

-. The increase of the epiphysorcrebral index during life in man.. 213
/. The resistance to the enrronrhment of the corpus callosum in

inaimnuls 21<>

3. Evidence based on the histology of tin- cpiphyseal complex 217

4. The relation of 1 he pariet al eye to t lie pineal body --1'1

5. The phylogenetic significance of the parietal eye \\ith reference to

vertebrate and invertehrate

8. Summary and conclusions i".s

9. Bibliography 210

1. INTRODUCTION

"Son siege au milieu de parties tres-importantes de 1'ence-
phale, sa Constance chez Fhomme et le vertebres, font pourtant
presumer que ses usages, s'ils ne sont pas d'un ordre aussi impor-
tant qu'on le supposait a 1'epoque des Esprits Vitaux, n'en sont
pas moins reels et tres-interessant a connattre."

Legros. These de Paris, 1873, page 24.

"Vix ulla unquam corporis nostri particula tantam famam
inter erudites non modo, sed etiam inter illiterates nacta est, ac
cerebri sic dicta glandula pinealis.'' These words written by
Soemmering359 in 1785 still hold true. Not only did this organ
attract much early medical attention, but its reputation was
extended by the metaphysicians and even further increased by
the satirical literature of an uncommonly virile period. Descartes
(1649) 89 in his discourse on the sources of the human passions,
expressed the belief that the pineal body was the seat of the soul.
This interpretation passed current during the epoch of Vital
Spirits. It did not, however, go altogether unassailed. Voltaire411
so successfully made it the subject of parody that his whim-
sical conception of the pineal body became more influential than
the origina hypothesis of Descartes. According to Voltaire,
the epiphysis should be regarded as the driver which, by means of
two nerve bands, guides the action of the cerebral hemispheres.
These nerve bands were long referred to by the anatomists as
"the reins of the soul."

During the past hundred years an increasing volume of re-
search has revealed the difficulties in the epiphyseal problem
and shown how far we are from a solution of it. In fact, the
views advanced by the students of this subject are so numerous
and often so divergent that any decision at the present time

5

6 FREDERICK TILM.V AND LUTHER F. WARREN

would seem ill-advised. The >eparation between those who
consider the pineal lx>dy a useless vestige and those who assign
to it extensive responsibilities in the sphere of internal secretion
i> too great to be reconciled on any but the most careful investi-
gation of the grounds for their differences. The phylogenesis of
the organ among the vertebrates, especially in its relation to
the third or parietal eye, as well as the significance of the struc-
ture as a possible mark of identification in the line of evolution
from the invertebrate to the vertebrate phylum, has raised many
perplexing questions. Although the researches of morphologists,
physiologists, and clinicians have established many significant
facts, it still remains to assemble this evidence as much in its
entirety as possible in order to furnish a satisfactory basis for
the discussion of the problem.

It is the purpose of this work to gather the recorded facts
concerning the pineal body and present them in several parts
under the following headings:

Part I. The morphology and evolutional significance of the
pineal body.

Part II. The physiology and pathology of the pineal body.

Part III. The clinical aspects of the pineal body.

THE MORPHOLOGY AND EVOLUTIONAL SIGNIFICANCE

OF THE PINEAL BODY

The morphological problem of the epiphysis may be for-
mulated in the following questions:

1. What is the significance of the pineal region in its relation
to the epiphysis?

2. Is the pineal body a vestige or is it an organ in some way
necessary to metabolism?

3. Does its structure furnish evidence of its function?

4. What relation does it bear to the third or parietal eye?

5. What is the phylogenetic significance of the parietal eye
with reference to the vertebrates and invertebrates?

Before submitting these questions to discussion, it seems
advisable to offer the evidence as much in extenso as is practi-
cable, having particular regard for historical sequence.

2. NOMENCLATURE

The pineal body was known to the Greeks and called by
them the 0-0^0. Kwoides and Kuvapiov because of its conical
shape. It was also termed the epiphysis because of its relation
to the rest of the brain. Latin authors refer to it as the turbo,
corpus turbinatum, glandula turbinata, glandula piniformis, glan-
dula conoides, conarium, penis cerebri, and virga cerebri.

Because of its resemblance to a pine cone, it was called by
Chaussier63 and Willis429 the corpus pineale. It has been called
by the Germans the Zirbel and Zirbeldriise, a designation which
doubtless has led to the more or less general use at present of
the term pineal gland. Several of the early writers called it the
glandula superior in contradistinction to the pituitary gland
which was referred to as the glandula inferior.

Since all of these terms were, in the main, devised to meet the
conditions in man and the higher mammals, it might be expected

7

FREDERICK TILNEY AND LUTHER F. WARREN

that they would not prove wholly satisfactory for some of frhe
lower vertebrates. Earlier works on the pineal body, even
such as dealt with ichthyopsid and sauropsid forms, employed
the terms epiphysis and corpus pineale with so little discrimina-
tion that these definitions became rather vague. The com-
plexity of the structure in the lower reptiles, in amphibia, and in
li>h is such that it may only in a very general way be denomi-
nated the epiphysis. In the first place, many of the forms just
mentioned present, instead of a single epiphyseal process, two
well-marked structures projecting dorsad from the roof of the
iiiterbrain. Ontogenetically, both of these processes are con-
nected with the epiphyseal anlage, and yet if one of them were
called the epiphysis which should it be and by what term should
the other be designated?

In a certain respect the suggestion of Hill ('91) m to call one
process the anterior epiphysis and the other the posterior epiphysis
has much to recommend it on morphological grounds. Unfor-
tunately, connotation has so rigidly associated the term epiphysis
with the much altered and modified conditions as they occur in
man and mammals, as almost certainly to lead to confusion in
the broader application proposed by Hill. More available,
although not without their defects, are the proposals of Studnicka
COG)386 according to which the posterior epiphyseal process
becomes the pineal organ and the anterior process the parapineal
onjiui. The use of the term pineal at once reverts to the mam-
malian forms, for description of which it was first employed.
To apply this term, as, for example, in the fish where it has no
descriptive value, cannot be in accord with the best morphologi-
cal tendencies. Yet to Studnicka should be accredited the most
thorough and extensive consideration of this subject; his defini-
tions may, for this reason, be regarded as standards, especially
if the desire to avoid new terms is kept in mind. Accepting
Studnirka's terminology of an anterior process, the parapineal
organ, and the posterior one, the pineal organ, it is necessary to
recogni/e certain subdivisions in each of these organs. The
pineal organ has an end-sac, a x/r///,-, and a />r».r/i/i<il portion, the
latter in some cases i- connected with the rest of the interbrain

THE PINEAL BODY 9

by means of a short, slightly constricted piece, the peduncle.
The parapineal organ, likewise, has an end-sac, a stalk, and a less
well defined proximal portion. Much variation exists in the
forms presenting these several parts — in many instances, one or
more of the parts described may be absent, yet, to make the
terminology as comprehensive as possible, all of these portions
should be included. Upon this basis the following constituents
may be recognized in the epiphyseal complex:

I. The pineal organ, consisting of:

1. An end-vesicle. 3. A proximal portion.

2. A stalk. 4. A peduncle.

II. Th.e parapineal organ, consisting of:

1. An end-vesicle. 3. A proximal portion.

2. A stalk.

The proximal portion and peduncle of the pineal organ cor-
respond to the epiphysis or corpus pineale of mammalian anat-
omy. The proximal portion is probably analogous to the cellu-
lar part of the pineal body while the peduncle is comprised
largely of nerve fibers.

3. GENERAL REVIEW OF THE LITERATURE

Galen (1576) 138 gave a description of the conarium in its rela-
tion to the third ventricle as well as to the chorioid plexus and
blood vessels about it. According to his interpretation, the
organ serves as the support for the great vessels converging upon
that portion of the brain. Oribasius (1554)285 mentioned but
did not describe the epiphysis. Uvarthonus401 believed that
delicate nerve fibers enter the pineal body; these fibers seem to
take origin in the lower portion of the spinal cord. Bauhinus
(1616)16 considered the conarium to be a glandular structure
related to the chorioid plexus. Diemerbroeck (1633) 91 showed
certain differences between the pineal body in man and in other
mammals. Dionis (1706) 93 described the pineal body as attached
upon either side to the chorioid plexus by a small band. This
band may be a nerve derived from the sympathetic system.

Ill FREDERICK TILM1Y AXD LUTHER F. WARREN

Duvernoy ( 1761), 10° in support of the theory of Descartes (1649), 89
claimed that the pineal body did not exist in the dog. Vicq-
d'Azyr (1781)408 observed the epiphysis in man, but could not
find it in fish. Stannius373 found it in all species which he ex-
amined and made a particular study of it in the salmon. In
this form he spoke of it as a highly vascular structure. Perrault306
found the epiphysis in the ostrich. Borrich and Harder38
observed the pineal body in the eagle. Malacarne258 found the
epiphysis in birds as did Cuvier ('45). 77 Bichat (1802)28 con-
>idered llie pineal bodj' a gland, and in it he found granules of
some calcareous substance. The general character of the
j tineal body is something like the cortical substance of the brain.
Soemmering (1785)359 gave an accurate account of the form of
the conarium and also its dimensions in man. In his descrip-
tion he confines himself largely to the fact that there occur in
the organ accumulations of a substance which he calls brain sand
or (icirrtilux ccrcbri. Soemmering noted many different condi-
tions under which this brain sand was apt to collect in the dif-
ferent parts of the pineal body. Haller (1768) 165 believed the
concretions were pathological and related to mental disorders.
Many observers made mention of calcareous concretions in the
pineal body, among them being Saltzmann, Ruysch, Meibomius,
Yieussens, Vicq-d'Azyr, Malacarne, Brunner, Kruger, Bartholin,
Winslow, Petermann, and Santorini. Parisini300 described the
pineal body in the camel, elephant, and lion, and Harder170 gave a
description of it in the dog. Carus (1814) 59 described the epi-
physis as having the form of a small peeked sac with almost no
nerve fibers in it. He was unable to find the organ in the sal-
mon. Chaussier63 described the form of the pineal body in some
mammals, suggesting that its shape compared to the pomme de
pin, which comparison led eventually to the adoption by the
French of the term corpus pineale. The Wenzels (1812), 42° in
their description of the pineal body, call attention to the fact
that the organ varies greatly in size according to the period of
life. Its size from the seventh year is augmented regularly
until middle life and then a successive diminution occurs until
old age. Acervulus cerebri is not found in the embryo nor in

THE PINEAL BODY 11

the fetus, but after the seventh year of life this element makes
its appearance and tends to increase until old age. Cruveilhier, 72
in his description of the conarium, drew attention to a cavity
situated near the base of the structure which frequently con-
tained a fluid. Gratiolet,157 referring to this cavity, described
it as the ventricle of the pineal gland.

Majendie, (1795)257 commenting at considerable length upon
the hypothesis of Descartes concerning the seat of the soul,
ingenuously remarks that he himself has a better conception of
the nature and function of the pineal body which he desires to
substitute for the theory of Descartes. His own suggestion,
says Majendie, is not only very simple, but actual and true, for
it must be obvious from the situation as well as from the struc-
ture and form of the pineal body that it serves as a tampon
designed to expand and in this way to close off the aqueduct of
Sylvius or, at other times, shrinking, to permit this aqueduct to
open again so that the fluid in the ventricles may have free
access from the third chamber to the fourth. Majendie, how-
ever, does not state upon what grounds the internal structure of
the pineal body justifies such a belief, but he is none the less
emphatic in calling attention to the valve-like nature of the
conarium with reference to the cerebrospinal fluid.

Gunz (1753) m attributed dementia to impeding of the flow of
spirits caused by the pineal body. Burdach ('19-'26)48 con-
sidered the pineal body as supplementary to both the cerebellum
and cerebral hemispheres. Tiedemann ('23)395 found the epi-
physis in reptiles, birds, and mammals. Serres ('24-'28)353 and
Willis429 both make the statement that the epiphysis occurs in
fish, birds, and reptiles — in fact, in all classes of vertebrates.
Andral ('29)4 also described the organ as occurring in all the
classes of vertebrates. Brandt ('29) 40 recognized a glandular
structure under a small scale in the head of Lacerta agilis which
corresponded to a circular depression in the parietal region of
the skull. This he regarded as a special gland. Milne-Edwards
('29), 107 in his researches on lizards, figures but does not describe
certain plaques in the head of these animals. He indicates these
as the occipital plaque, the parietal plaque, and the interparietal

12 FREDERICK TILNKY AM) LUTHER F. WARREN

plaque. The latter is a black spot correspond in g exactly to the
position of the pineal gland. Duges ('29) 97 also figures the
>ame appearance in certain lizards. As early as 1835 Hollard188
had made the observation that the epiphysis was entirely nerv-
ous in structure. He is also authority for the statement that
this body does not occur in fish. Gottsche ('35), I54 however,
stales that the pineal body does exist in all fish. Valentin ('43)403
concurred in Hollard's idea, although he was of the opinion that
the elements in the pineal body differed considerably from tin-
gray matter of the brain. Guillot ('84)16° makes the statement
that, although the pineal body exists in all vertebrates, it is not
until the reptiles are reached that the pineal apparatus makes
its appearance in most complete form. Regule"as ('45)325 recog-
nized that in man the pineal body, both in its volume and form,
was variable.

Observations concerning the structural character of the pineal
body were made at a remarkably early period. It was not,
however, until the methods of histological technique were fairly
well advanced that much attention was devoted to the minute
structure of the conarium. Kolliker ('87)212 observed two
types of cells in the pineal body; that is, small round cells and
niultipolar nerve cells with compact bundles of nerve fibers.
These latter were few in number. From his observation Kolliker
was led to believe that the pineal body is entirely nervous in type.
Clarke ('60)r'9 found nerve fibers, nuclei, and brain sand but no
nerve cells in the pineal body. He also observed a reticular
structure which resembled the olfactory mucous membrane.
The arrangement of the cells, he believed, was similar to that of
the fourth layer of the olfactory bulb in sheep and cats.

Faivre ('55)ni was among the first to make an extensive com-
parative histological study of the pineal body. He examined the
minute -tructure in man, horse, guinea-pig, dog, ox, rabbit, pig,
hen, 1 urkey, dove, and tortoise. As a result of his observations,
lie recognized three elements in the human pineal body: first, a
fibrovascular envelope; second, a globular parenchyma, and.
third, acervulus cerebri. Faivre is in general accord with
Valentin, in that the pineal body differs essentially from the

THE PINEAL BODY 13

rest of the nervous system and has an appearance strikingly
ike the pituitary gland. He, apparently, was first to recognize
that the cells of the epiphysis contained granules in their cyto-
plasm. These he called parenchymal cells. He also observed
that these cells were smaller in childhood than in adult life and
concluded that the parenchyma of the pineal body is composed
of a large number of globules. The globules are generally
elliptical and irregular in shape. Faivre believed the globules
to be the nuclei of the cells, and to him must be accredited the
first observation of these cellular characteristics of the pineal
body.

Marshall ('61) 261 made some observations concerning size,
\. -eight, and sand-content in a chimpanzee. Schmidt ('62)347B
showed the continuity of the epiphysis with the brain in the
human fetus and its relation as an evagination of the encephalic
roof. Stieda ('69) 376 studied the pineal body of birds and mam-
mals and described anastomoses of the cytoplasm of the cells
in the form of a reticulum. Luys ('65)253 advances an ingenious
conception concerning the nature and connections of the pineal
body. In his opinion, this organ is a mass of gray substance
pertaining to the central gray matter surrounding the third
ventricle and having the same histological characters. He
claims that originally in the human embryo the structure is
bilobed like the mammillary bodies and that, therefore, it should
be considered as a transitory bilobed structure, a true posterior
mammillary body which has fused across the median line. Luys
concludes that the gray substance of the conarium, the hippo-
campal convolution, and the mammillary tubercles form with
the anterior pillars of the fornix a complete system. The mammil-
lary bodies and the conarium are centers of reception for fibers
convergent from the hippocampal convolution. Efferently these
centers are connected with the optic thalami. Luschka ('67) 252
noted the presence of fibers in the pineal body of man. Frey
('67) m believed that the pineal body was made up exclusively
of nerve tissue. He found in the adult the following elements:
1) multipolar ganglionic cells; 2) round cells with prolongations,
and 3) isolated nerve tubes. Leydig ('68) 232 states that the

14 FREDERICK TILNEY AM) LUTHER F. WARREN

pineal body in the mouse resembles the pituitary body in reptiles
with certain small differences. Meynert ('77)271 expresses the
opinion that the parallelism between the pineal body and the
pituitary body is a mistaken idea. He believes that the epi-
physis should be considered a ganglionic derivative of the teg-
mentum. It contains two types of cells, namely, those with a
diameter of 15 micra and those with a diameter of 6 micra. The
pineal body, in Meynert's opinion, differs from other ganglia
only in the fact that the cells are very close together. Krause
('76)218 observed in the pineal body nerve fibers having a double
contour. Henle ('71) m described the parenchyma of the pineal
body as subdivided by fibrous processes called septa such as
occur in lymph glands. These divisions gave rise to more or
less independent follicles or acini varying in size from 6 micra to
30 micra in diameter. It was Henle's opinion that the pineal
body resembles more exactly lymph glands than any other
tissue in the body. Stieda ('Go)375 in several species of amphibia
observed an epithelial structure between the eyes in the frontal
region of the head which he called the frontal cutaneous gland.
Subsequent investigation revealed that this so-called cutaneous
gland was in fact a portion of the epiphyseal complex. Paw-
lowsky ('74)305 described fibers in the epiphysis which seemed to
be derived from the posterior commissure. Huxley ('76) 191
described the pineal body in Ceratodus forsteri. In this form
it occurs as a slender, cylindrical body. Baudelot (70) 14 gave
a detailed description of the pineal body in Gadus merlangus.
He also found it in the salmon and in the Cyprinoids. Camper,55
although he observed it in many fish, was not able to find it in
haddock or cod. Arsaky8 was unable to detect the pouch of
the pineal body in fish. Haller (1768) lf>5 did not observe the
pineal body in birds nor did he observe it in the pike or trout.
He <li<l find it, however, in the carp and tench.

Owen's ('81)293 vie\v of the conariohypophyseal organs is such
that it at least deserves comment, if only as a historical curiosity.
Accord ng to Owen, the central nervous system in annelids forms
a ring through which passes the oesophagus (cesophageal ring1.
In higher vertebrates, especially in embryonic life, the nervous

THE PINEAL BODY 15

system manifests this same disposition, for here, the brain curves
itself backward in such a way as to constitute a ring above the
region destined to become the mouth, thus producing a deep
fossa directed toward the brain. Owen regards this as part of a
canal which traverses the brain, now disposed as the cesophageal
ring of articulates. Early, however, the process is arrested and
the tube-like invagination comes to form the pituitary gland.
The original tube from the mouth region is completed by an
invagination from the dorsal region of the head which is con-
nected with the skin. This element becomes atrophic and its
remains constitute the pineal gland. Baraldi ('84) 13 modified
the theory of Owen by stating that the hypophysis was a deriva-
tive of the wall of the mouth of the gastrula or, in other words,
the last vestige of the extreme anterior portion of the alimentary
canal of worms. Robin's334 idea seemed to offer some confirma-
tion to this opinion in the fact that he found in the epiphysis,
upon microscopic examination, a follicular, gray substance con-
taining a granular liquid very similar to that in the intestines.
Schwalbe ('81)348 found medullated nerve fibers which ac-
company the blood vessels and come into relation with bipolar
and multipolar cells in the pineal body. He believes there
existed some similarity between the pineal body and lymph
corpuscles, but regards the cells of the former to be modified
epithelial elements. Ganser ('82) 142 thought the pineal body to
be an unpaired process of the ganglion habenulae. Flechsig
('83) m maintained that the epiphysis sends fibers to the fascicu-
lus retroflexus. Sappey ('87) 344 considered the pineal body
analogous to the substance of the cerebral cortex. Mingazzini
('89) 276 regarded the elements of the pineal body as similar to
those of the lymphatic corpuscles. Moller ('90), 278 investigat-
ing the epiphysis in the chimpanzee, distinguishes an unpaired
peduncle which constitutes the largest part of the pineal body.
The organ itself is 3 mm. x.2 mm. long. The peduncle is 4 mm.
long and consists of nervous tissue. The pineal recess is ex-
tensive. Moller regards the structure as a rudimentary organ
in a retrograde state. Charpy ('94)62 considers the epiphysis as
a degenerating organ made up exclusively of epithelial elements

ll'i FREDKHICK TII.M.Y AM) LUTHER F. WARRKX

.•ml some nerve fibers. I )el>ierre ('94)84 believes the pineal
body t<> be a blood vascular gland with many degenerated
dements. Lotheissen ('!)4 .)-•"•" studying a large number of mam-
mills, recogni/ed in marsupials < Man-upa* t/nju/ilii/s) some
libers of the fasciculus retrollexus which penetrate the pineal
body, also some fibers which leave the summit of the epiphysis
which he believes represent the remains or rudiment of the
parietal nerve in reptiles. Cajal ('95)53 thinks that the nerve
Jib; rs in the pineal body are sympathetic and the body itself
is a blood vascular gland. Condorelli-Francaviglia ('95) 70 in
studying the brain of a marsupial (Halmatunts dorsal is), noted
in consequence of poor development of the corpus callosum that
the pineal body was only 2 mm. long and 1.5 mm. wide. Heitz-
mann ('96)169B described the epiphysis as composed of gray
substance. Staderini ('97)372 investigated the development in
many mammals. Soury ('99)365 described connective tissue
septa dividing the pineal body into compartments which are
occupied by a second tissue resembling adenoid tissue in which
; re round cells and cells with long prolongations. Bechterew
('00)2° found evidence of nerve fibers passing from the posterior
commissure to the peduncle of the pineal body. Zancla ('06)432
studied the histology of the epiphysis in man. He observed
cells in the parenchyma which consist of a scant protoplasm and
large nuclei. These cells have a stellate form and prolongations
which often bifurcate at acute angles and then ramify still
further. The cells lie in a mesh of fibrils apparently nervous
in character. By the methods of Cajal, Weigert, and Biondi,
he \\as unable to interpret these cells either as nerve elements
or as glandular cells. He believed they are of a neuroglial
character and advances the hypothesis that they have an internal
secretory function. Around the calcareous concretions he found
nccrobiolic areas. Uomiti ('82)33G studied the development of
the epiphy-i- in the rabbit. Anglade and Ducos ('08)5 found
ill'1 organ made up mostly of neuroglia in man.

THE PINEAL BODY 17

4. THE COMPARATIVE MORPHOLOGY OF THE PINEAL REGION

To make the proper evaluation of the pineal body this organ
should be considered in relation to its immediate encephalic
environment. Indeed, any study of the pineal organ which
omitted this environment would give but an inadequate view of
the epiphysis. A number of structures make their appearance
in connection with the roof-plate of the forebrain. Some of these
have a marked constancy; some are transitory, making their
appearance in one or two classes of vertebrates only, yet all of
them have a definite, phylogenetic significance in connection
with the epiphyseal complex. Embryologically, the roof-plate
of the primitive forebrain vesicle, that is, the prosencephalon,
gives rise to a number of evaginations. Certain of these even-
tually become prominent, adult organs. The most conspicuous,
both because of its constancy throughout the phylum and
its numerous adaptations, is the pineal or epiphyseal complex.
It has been suggested that the structures which form the roof
of the interbrain be known collectively as the pineal region.
This suggestion made by Minot ('01) 277 offers a convenient term
for the identification of a complex area of the brain. According
to Minot, the pineal region begins at the lamina terminalis or
lamina neuroporica which is its cephalic limit and comprises the
following elements:

1. The paraphyseal arch.

2. The velum transversum.

3. The postvelar arch, also known as the dorsal sac.

4. The epiphysis, also known as the corpus pineale.

5. The posterior commissure.

Minot' s specification of the pineal region needs some extension
in order to meet the requirements of all classes of vertebrates.
The following description of the pineal region niakes provision
for all of the elements which may and in some instances- do
appear in this area of the brain.

Paraphysis. The paraphysis is an evagination situated at
the extreme cephalic end of the forebrain roof-plate. Ventrally
it is continued into the lamina neuroporica. Dorsally it is con-
tinuous with the velum transversum. Minot assumed that the

MEMOIR 9

18 FREDERICK TILNEY AND LUTHER F. WARRKX

pineal region develops a series of structures which seem to be
directly concerned with the formation of the fluid in the cavities
<>(' the brain. He holds that the chorioid plexus supplies the
main bulk <>f this fluid, but the gland-like organization of the
paraphysis indicates that it may supply a secretion of special
chemical substances to the encephalic fluid. The organ reaches
its highest degree of development in amphibia, where it become-
a large, complicated, glandular structure with a central canal
from which a complicated set of anastomosing tubules are given
off. It has a well-marked sinusoidal type of circulation. These
conditions have been observed by \Varren"" in Xir,<l<»i, \«--
lnrus, Proteus, Siren, Ichthyophis, Tritnn, R'uni, Amblystojnn,
and Diemyctylus. The paraphysis has a well-developed,
glandular character in amphibians and lizards; in birds it is
reduced to a single, thick-walled outgrowth of small dimensions.
Selenka3-"12 in 1890 observed the organ in opossum; it has also
been observed by Warren ('17)417 in the sheep, and also by
Francotte127 in 1887 in the human embryo. The paraphysis is
much reduced in the upper and lower ends of the vertebrate
series, while in the middle, especially in amphibia, it is much
developed. In amphibia its character is glandular, as it is also,
to a, less degree, in reptiles.

The paraphysis was erroneously regarded as the conariuin by
Selenka ('90). 352 It has also been called the anterior epiphysis
by Burckhardt ('90)-12 and the pre-paraphysis by His ('68). 182
Sorensen ('94),3r>3 called it the posterior chorioid plexus.

'I' he, velum transversum. This is a transverse furrow, imme-
diately caudad to the paraphysis, which projects into the ventricle
and >eparates the paraphysis from the dorsal sac. In some
instances this furrow is simple and flat, but in others it is thrown
into many subsidiary folds and becomes highly vascular in the
form of ;i plexus. In some forms, as in Peiroinyzon, it is alto-
gether wanting, and under such circumstances the paraphysis
passes over without sharp line of demarcation directly into the
dorsal sac. In Chimaera there is a lack of the velum and also
a small paraphysis so that the dorsal sac seems to pass over
into the lamina snpraneiiroporica without demarcation. In

THE PINEAL BODY 19

Dipnoians the velum presents a pair of folds or it may develop,
as in certain amphibia, as an unpaired chorioid plexus.

The dorsal sac. This element of the pineal region was called
the Zirbelpolster by Burckhardt42 in 1890, the parencephalon
by Kupffer22 in 1887, and the post-paraphysis by Sorensen362
in 1893. Goronowitsch ('88) 153 appears to be the first to apply
to it the term dorsal sac. This sac is a dilated vesicle usually
extending far above the roof-plate. In mammalia, however,
in those forms in which the corpus callosum has made its appear-
ance, the. sac becomes much flattened and is difficult to recognize
because of the altered condition consequent upon the develop-
ment of the corpus callosum. The walls of the dorsal sac are
lined internally by ependymal cells. In many instances these
walls may be thin and definite or quite thick, containing many
folds which may or may not be vascular; in certain instances
these folds attain such a vascularity that they resemble a chorioid
plexus.

The pars intercalaris anterior. The more caudal portion of
the dorsal sac as it approaches the level of the roof-plate may
become much thickened and contain a dense mass of neuroglia
tissue. Usually this intercalated portion is not of any great
extent. It appears only in a few forms.

The commissura habenularis. This element was called by
Osborn288 in 1884 the superior commissure and by Gottsche in
1835154 the commissura tenuissima. It affords a connection
between the two ganglia habenulae. In some cases, as in Petro-
myzon, the connection established by this commissure is such as
to include the mass of the two ganglia in the general commissural
region. In the immediate neighborhood of this commissure and
coming into direct connection with it is often seen the ending of
the nerve from the parapineal organ. This is particularly the
case in Saurians, and it is by this means that the so-called parietal
nerve makes its connection with the brain. Its fibers may be
traced in some instances as far as the ganglia habenulae.

The epiphyseal complex. This complex comprises two distinct
elements, a pineal and a 'parapineal organ. The pineal organ
may consist of an end-sac or terminal vesicle, a stalk, a proximal

20 FREDERICK TILXKV AND LUTHER F. WARREN

portion, and a peduncle. In all probability the proximal por-
tion of the epiphyseal complex gives rise to the epiphysis cerebri
or what has been called the pineal gland. In some forms nerve
fibers have been found making their course through the stalk of
tlii-- pineal organ and have thus given rise to the term nermx
l>i in tills. The paraj )incal organ is the second, though less con-
stant, portion of the epiphyseal complex. When present, it also
consists of an end-vesicle, a stalk, and a somewhat dilated
proximal portion. Most of these evaginations contain cavities
which are in communication with the third ventricle. The
recess which connects the pineal organ with this ventricle is
known as the recessus pinealis.

The pars intercalaris posterior. The caudal wall of the proximal
portion of the pineal organ often shows a marked increase in
thickness as it approaches the level of the diencephalic roof.
This thickening interposes an area between the proximal portion
of the pineal organ and the posterior commissure. Often this
intercalated part shows considerable dimensions. In the forms
in which it is most developed, the fibers of the pineal nerve may
be seen to enter this intercalated portion in the roof of the inter-
brain. It has been called the pars intercalaris by Burckhardt
in 1890,42 but the necessity of designating it the posterior inter-
calated portion becomes obvious in view of the fact that an
anterior structure of like character has already been described.

The posterior commissure. The last and caudalmost struc-
ture in the roof of the interbrain is the posterior commissure.
This has already been assigned by Minot in 190 1277 to the mid-
brain, but the fact that certain fibers from the tractus pinealis
and the nervus pinealis may be traced into direct relation with
this commissure seems to ally it more with the derivatives of the
roof-plate in the interbrain region rather than that of the mesen-
cephalon.

The homology of all of these parts in the roof-plate of the
prosencephalon has been given for the different classes of verte-
brates by Burckhardt in 1890'12 in his work on I'mln/ilt-rux and
aiiain in his work (45) on the structural plan of the brain. With
this view of the generalized plan of the pineal region in vcrte-

THE PINEAL BODY 21

brates, it will now be possible to consider in detail some of the
variations which the region presents in the different classes.

1 . The pineal region in cyclostomes

In cyclostomes the absence of the velum transversum causes
the paraphysis to pass over into the dorsal sac without sharp
line of demarcation. In fact, it is difficult to make out with
any degree of certainty a true paraphyseal process. What
there is of a paraphysis is a small evagination from the most
cephalic portion of the dorsal sac, and the morphological lines of
differentiation are such as to leave it still open to doubt whether
there is an actual paraphysis in these forms. Studnicka ('99) 388
is authority for the statement that such an organ does exist
in Petromyzon. In Ammoccetes the epiphysis is more clearly
defined. The lamina supraneuroporica in cyclostomes is more
specialized than in other vertebrates. In the most dorsal por-
tion of this membrane there occurs a thickening which lodges
fibers passing in a transverse direction and constitutes a com-
missure known as the commissura pallii. The dorsal sac is un-
usually high and deflected in a cephalic direction as a result of
the pressure put upon it by the pineal and parapineal organs.
Its dorsocaudal wall shows a marked invagination as a result of
the pressure not only of the epiphyseal complex, but also of the
ganglion habenulae. No chorioid plexus or other vascular for-
mation appears in direct connection with either the paraphysis
or the dorsal sac. The pars intercalaris anterior is absent, but
a very massive commissura habenularis is observed in all forms,
making its appearance early in the course of development.

The epiphyseal complex presents a pineal organ and a para-
pineal organ. Both of these lie in close apposition to each other
extending cephalodorsad in such a direction that their terminal
portions come to overlie the dorsal sac. The dorsal wall of the
pineal organ lies immediately beneath the frontal region of the
skull. The posterior intercalated portion is also absent, but a
large posterior commissure occurs in all forms. The pineal, as
well as the parapineal organ, possesses a nerve, that connected

L'L' FREDERICK TILNKV AM) LUTHER F. WARREN

with the pineal organ, the so-called pineal nerve, ends in the
po-terior commissure, while the p;ir;ii)ineal nerve has its termi-
nation ni the commissura habenularis.

Probably the first observation upon this region in the cyclo-
stomes was made by Serres3-"'3 in 1S25. Other contributions fol-
lowed by Schlemm and d'Alton 347f in 1838. Johannas Miiller-"0
in ls:;s and Siebold and Stannius3:>:> in 1854 added their studies
of this region. Mayer-1'-"1 in 1S(>4 mentioned the occurrence of

EpuL Cor

Po

Schd

. 1 Schematization <if pincul region in Cyclostomes, iicconliujr to Stud-
nicka, l(.tii">.

L«., lamina terminalia; /'/. p.-napliysis; /'/»., para pineal oi^an :/'«., pineal or.iiau ;

Ef a., habenular ganglion; Th., p.-u-apincal aervejCA., commissura lialicnulari^ ; // .
recessus pincalis; ('/>., oonnnis.-iua posterior; «., Xfiin., norvus pim-alis.

m.-iny calcium corpuscles in and about the pineal origin. Wie-
dcrsheini'1-- in 1880 spoke of the epiphysis as a, small, saccular
body, hut it was not until 1883 that Ahlborn- first described the
microscopic appc.-iranccs of th<' epiphyseal oompl(»x in which
he was able to observe two superposed vesicles. Ahlborn,
however, did not interpret these two vesicles as independent
evaiiinations from the roof of tin' interbrain, but considered
them as subdivisions of the epiphy>is.

THE PINEAL BODY 23

Later, Beard ('87)17 and Owsiannikow ('88)295 following Ahl-
horn's lead, both spoke of two epiphyseal vesicles. Studnicka
('99)388 and Kupffer ('94)224 showed that these two -vesicles were,
in fact, independent parts of the epiphyseal complex. Studnicka
called the anterior vesicle the parapineal organ and considered it
homologous to the parietal eye of reptiles. This he later con-
firmed in a subsequent work. Kupffer, however, saw in the
parapineal organ or parietal eye of reptiles the homologue of the
paraphysis in Petromyzon. Retzius ('95)331B was the first to
employ the Golgi method in Petromyzon and Ammoccetes.
By this means he was able to demonstrate the nerve elements
of the stalk of these two epiphyseal organs. The finer structure
of the pineal and parapineal organs in Petromyzon marinus was
given by Leydig in 1853231 and Studnicka in 1899, 3S8 while Johns-
ston in 1902195 described these organs in Lampetra wilderi.

2. The pineal region in selachians

The pineal region in selachians is very similar to that of
Petromyzon with the exception that in the epiphyseal complex
the parapineal organ does not appear. The selachians are
remarkable for another fact, namely, that one member of this
class, Torpedo, develops no part whatsoever of the epiphyseal
complex; that is to say, both the pineal and parapineal organs
are wanting.

In Notidanus, Burckhardt in 189042 distinguishes the follow-
ing parts: At the dorsal extremity of a thickened and invagi-
nated lamina neuroporica there appears a slightly developed
paraphysis. Immediately following this in the roof-plate there
is a marked invagination defining the velum transversum, which
appears in these forms as a simple infolding of the roof-plate
without any vascular development. The dorsal sac presents
itself as a more conspicuous element in the roof of this species
than in the cyclostomes. There is no anterior intercalated
portion and the epiphyseal complex shows only the presence of
the pineal organ. A short pars intercalaris posterior has been
described followed by the posterior commissure. This descrip-
tion given by Burckhardt in Notidanus holds true for most of
the forms of selachians with the exception of Torpedo.

FHKDKHICK TILNKV AND LUTHER F. WARREN

d'Erchia ('96) 109 differentiated in Pristiurus the same elements
as in Notnlinins. but in Torpedo he found that the epiphyseal
complex was entirely wanting. He further observed that the
development of the velum transversum occurred much earlier
than the pineal organ. Minot ('Ol)277 maintained that an actual
paraphysis does not develop in selachians. In comparing the
1 tinea! regions of cyclostomes with selachians, the most striking

Po-—

Fig. 2 Schematization of pineal region in Selachians, according to Studnicka
1905.

L.s-.. lamina tcrniinalis; Pf., paraphysis; V. velum transversum; D.s1.. dorsal
sac: !'•>., pinoal organ; St., stalk of pineal or^an; Ch., commissura halicnul.-iris;
/.' . recessus pinealis; Cp., commissura posterior; Sclt., pars intercalaris posterior;
Prox., pniximal portion; '!'/>., Iractus pinealis.

appear to be in the extreme development of the
parapineal and pineal organs in /'ilro/ni/zon and allied forms,
while the parapineal organ is ah-ciit in selachians. Further-
more. the absence of any distinct velum transversum in cyclo-
si. mies makes the presence of a definite paraphysis extremely
doubtful, while the velum transversum in selachians differen-
very clearly a fairly well formed paraphysis. The pineal
in Elasmdbranchs is much shorter than in Petromyzon.

THE PINEAL BODY 25

Of the early workers upon the selachian pineal region, Jack-
son and Clarke (75)193 appear to be the first to make mention of
the actual pineal organs as they occur in these forms. They
described this region in the brain of Echinorhynus spinosus.
According to their description, the structure was a small pro-
jection extending fro'm the roof of the interbrain to the surface
of the skull. Ehlers108 in 1878 gave the first detailed description
of the relation of these parts in Acanthias and Raia. Balfour
('78) 10 in the same year described the embryological development
of the pineal region in selachians. Cattie ('82) 60 gave the de-
scription of the pineal organ in a large number of Elasmobranchs.
Carrington ('90) 58 described the organ in Larnna cornubica and
Galeotti ('96)14° employing certain cytological methods in his
investigations of the pineal region, gave an important description
of these parts from a histological point of view. d'Erchia's
work on Pristiurus and Torpedo has already been referred to.
His was the notable observation that the epiphyseal complex
was entirely absent in Torpedo.

3. The pineal region in ganoids

This region in ganoids is characterized by the presence of the
usual elements with the exception that the parapineal organ does
not develop. In A mia alone is there any rudiment of an anterior
portion of the epiphyseal complex, and even here it is so slight
as hardly to justify the attempt to homologize it with the para-
pineal organ in Petromyzon. Goronowitsch ('88) 153 and Kupffer
('93) 223 described the pineal region in Acipenser and recognized
in it all of the parts usually observed in this area of the brain.
Following a broad lamina supraneuroporica there is a well-
marked paraphysis which at first is truly membranous but subse-
quently becomes highly vascular and takes on the form of a
tubular gland eventually concealing the great part of the lamina
terminalis. In certain forms, as in Polyodon, the paraphysis,
although well developed, is relatively much smaller than in
Acipenser. The next element in the forebrain roof, namely,
the velum transversum, is broad and much convoluted although
not very highly vascular. The dorsal sac presents the form of a

L'li FREDERICK TILXKV AM) LUTHER F. WARREN

largo evagination, generally membranous, and in several forms
having marked prolongations. Tims in Arniu there are two such
prolongations, the more dorsal of which extend- as far back as
the midbrain, while in 7W///;/r/-//N a prolongation of the dorsal
sac arches over the midbrain and extends as far caudad as the
cerebellum. Xo anterior intercalated part is present in the
ganoid, but a well-marked habenular commissure is present
immediately cephalad of the epiphyseal complex. This latter
consists of a single evagination from the roof-plate. Theanterior
epiphyseal element is absent in the ganoid so that the pineal
organ alone is encountered in this region. Immediately follow-
ing the latter structure is a short pars intercalaris posterior and
then a large posterior commissure.

The pineal region in ganoids differs from that in selachians
mainly in the presence of a large and glandular paraphysis; also
in tbe existence of an unusually large and extensive dorsal sac,
prolongations of which are apt to extend far beyond the usual
limits of this structure, even arching over the midbrain and
reaching the cerebellum.

Of the early works upon ganoids, Salensky341 in 1SS1 first
gave a description of the development of the pineal region in
Acipcnser. Accounts of the ontogenesis in this same form were
later given by Owsiannikow ('90)297 and Kupffer ('93). 2M Bal-
four and Parker ('82)12 gave a description of the development of
this region in Lepidosteus. Hill ('94)18° contends that th-:re are
two epiphyseal outgrowths from the roof of the interbrain in
Amia calva. The more anterior of these two outgrowths or
vesicles, Hill thinks, is homologous with the parietal eye of
Lacertilia, and he further maintains that it is extremely prob-
able that the two vesicles in their primitive posit ion were side by
side, thus indicating the existence of two organs which in the
primitive form, like the lateral eyes, were arranged as a. pair for
Mime definite function. Eycleshymer and Davis f97)113 con-
firmed the findings of Hill and added the further important
observations that in the late embry.mir state nerve libers could
be seen connecting the commissure habenularis with the para-
pineal as well as Hi-- pineal organ.

THE PINEAL BODY 27

4. The pineal region in teleosts

In teleosts the parapineal organ does not appear and the
pineal organ itself is present only in a seemingly retrogressive
condition. During the early stages of development, however,
in a few forms there is an anlage of the parapineal organ. The
lamina supraneuroporica is, if anything, more broad and more
pronounced than in the ganoids, but it differs from this structure
in the latter forms in the fact that it is not vascular nor does it
come into relation with any vascular network. A paraphysis
does not develop, as a rule, or if it does occur, it only appears
as a small evagination from the roof-plate, as in Belone acus.
Not infrequently in the earlier stages of development in Lophius,
the paraphysis appears as a small bud in the roof region. In
the larval forms of some species, as, for example, Anguilla and
Cepola, the paraphysis has the form of a very small evagination
from the roof consisting of a thin wall, but is not vascular and
in no way connected with a vascular net. The velum trans-
versum is a simple, flat, transverse fold which is not in connec-
tion with the chorioid plexus in any portion. In certain in-
stances this element is very little developed and may, in a few
cases, be entirely absent. The dorsal sac is, as a rule, very large
and presents itself in several different' forms. Frequently it is
thrown into many folds, particularly the portion representing
the superior wall and in these folds are found numerous blood-
vessels in a plexiform arrangement. Sometimes the sac along
its caudal wall is grooved in the midsagittal plane and in this
groove rests the stalk of the pineal organ. An anterior inter-
calated portion is absent, but a well-marked habenular com-
missure is always observed. Following this commissure is the
pineal organ and caudal to it a short pars intercalaris posterior
followed by the posterior commissure (fig. 3).

Among the early workers in this region in teleosts are listed
some of the great pioneer names in morphology. Alb'recht
Haller in 1768165 described the epiphysis in the carp, but did
not find it in the trout. Cuvier in 184577 also observed it in
teleosts, and Carus in 181459 found it to be a saccular formation
extending from the dorsal region of the brain. Tiedemann394

FREDERICK TILXEY AXD LUTHER F. WARREN

in 1816 could not find it in the bony fish, while ( iottsche154 in
1835 found it in these animals, but thought that it was connected
by blood vessels or a membrane with the ganglion habenulae
and the commissura habenularis. Mayer in 1S64265 gave a
description of the epiphysis as being merely a vascular convolu-
tion in the roof of the interbrain, while Owen294 in 1866 was not
at all sure of its existence even as a vascular convolution of the
roof-plate. In 1870 Baudelot14 described the epiphysis as a

vf

Tp Sch Cp

Fig. 3 Schematization of pineal region in Teleosts, according to Studnicka,
1905.

/>.s-.. lamina terminalis ; Pf., paraphysis; Ds., dorsal sac; P., velum trans versum;

('h., ronmiissura habenularis; Po., pineal organ; Si., stalk of pineal organ; 7'/'.,
tr;ietus pincalis; Sch., pars intercalates anterior; Cp., commissura posterior; M.
midbrain.

round or pear-shaped body bet \veen the lobi optici. The first
exact description of the organ was given by Rabl-Riickhard819
in ISXo on the basis of microscopic sections. Cattie60 in 1882
described the gross appearances of the organ in a large number of
leleosis, and Hilllso in 1894 gave one of the most detailed and
reliable accounts of this region in teleosts, basing his description
on \\\> findings in salmon. Other excellent descriptions of the
onfall in teleosts have been given by Ussow ('82), 402 Leydig
'96 . and Ilandrick ('(I!

THE PINEAL BODY 29

The work of Galeotti140 in 1896 on these forms is of particular
interest. This observer,, applying certain means of cellular
differentiation in the technique, showed that some cells of the
pineal organ give definite evidence of secretory activity. In
Leuciscus he found that the nuclei of the cells contained fuch-
sinophile granules and also that the nucleoli in these nuclei
were often extruded and later appeared in the protoplasm of the
cells. The product of such secretion in Galeotti's opinion was
delivered to the cavity of the organ.

The chief difference between the pineal region in ganoids and
teleosts lies in the fact that in the latter forms the paraphysis is
entirely absent while in ganoids it constitutes a conspicuous
element.

5. The pineal region in dipnoi

In dipnoi the only portion of the epiphyseal complex which
develops is the pineal organ and this is much less well defined
than in the lower forms. No anlage of the parapineal organ
makes its Appearance. The paraphysis develops later than the
pineal organ. The lamina supraneuroporica, according to
Burckhardt ('90), 42 as it appears in Protopterus, is very thick
and well developed. The absence of any well-defined velum
transversttm makes it appear as if the paraphysis were an an-
terior division of the dorsal sac, and yet a paraphysis may be
said to exist in these forms, although no sharp line of demarca-
tion may be drawn between it and the dorsal sac. The para-
physis itself presents a number of transverse folds beginning in
the attenuated membrane immediately dorsal to the lamina
supraneuroporica. In Ceralodus the entire paraphysis has the
appearance of a glandular structure, the lumen of which is in
connection with the ventricle of the brain by means of a small
canal. Although an actual velum transversum does not, in the
strict sense, exist, Kerr ('03), 202 in Lepidosiren, and Studnicka
('95, '96), 3S6 in Ceratodus, have both described several folds in a
position dorsal to the paraphysis. The dorsal sac is but little
developed, although it does appear as a membranous structure
extending from the roof of the interbrain. No pars intercalaris

:•><) FREDERICK TILXKV AM) LUTHER F. WARRKX

anterior is observed, but there is a well-marked commissura
habenularis as well a> the pineal organ, a posterior intercalated
portion, and the posterior coimnissure.

The earliest work upon this region of the dipnoi was by
Huxley1"1 in ls~(>. In this he described the pineal organ as a
cylindrical structure which had a cordiform enlargement at its
distal extremity. This latter lay deeply seated in a small exca-
vation of the cartilaginous skull roof. Wilder-4'-7 in 1887 show.-d
an unusually large paraphysis in Ceratodus, but did not observe
the pineal organ. Sanders343 in 1889 saw the end-vesicle of the
pineal organ in the form of a small body situated above the
chorioid plexus' of the interbrain. Studnicka ('95, '96), 386
distinguished in Ceratodus a dorsal sac and a paraphysis, the
former lying closely compressed against the latter. He also
observed a pineal organ with a long stalk which lies in a fold
along the superior wall of the dorsal sac, while the end- vesicle
is situated above the paraphysis. In Protopterus annectens,
Wiedersheim ('80)423 and Beauregard ('81) 1>9 mistook the dorsal
sac for the pineal organ, and Fiilliquette ('86)132 was unable to
distinguish between the ganglion habenulae and the pineal
organ. The erroneous identifications made by these authors go
to show the great difficulties which the pineal region in dipnoians
presents. It was not until 1890 and 1892 that Burckhardt1-'"44
first gave the proper description of the pineal organ in these
forms.

6. The pineal region in amphibia

In I'rodela and Apoda only the pineal organ develops and
this in but an extremely rudimentary form. The portions of the
j)ineal organ which are present in these forms represent the
proximal part of that structure. In no other group of verte-
brates is the pineal organ so little developed; it presents itself as
a sac lying close to the interbrain, the lumen of \\hich is sub-
divided into numerous branches. de(!raafi:>5 in 1886 was first
to recogni/e this condition and describe it in amphibia.

In Anura, as in I'rodehi and Apoda, the pineal organ only
develops. It usually consists of the proximal saccular part of

THE PINEAL EOD\ 31

this structure and the end-vesicle. The latter constitutes the
cutaneous gland. These two parts, connected by a stalk of fine
fibers which lead to the brain roof as the tractus pinealis, are the
distinguishing features of this region in Anura. The proximal
part alone in Anura is the homologue of the very rudimentary
organs observed in Urodela. The pineal organ of the frog's
brain has often been mistaken for the highly developed chorioid
plexus, for the paraphysis, or for the dorsal sac. Such errors
have been made by Wymann431 in 1853, Reissner328 in 1864, and
Stieda379 in 1875. Goette151 in 1873 first recognized the proximal
portion of the pineal organ and called it the epiphysis. This he
observed in the early stages of development in Bombinator.
Gravenhearst158 many years before this found the distal part of
the pineal organ in the head of Rana subsaltans, situated in
relation to a light colored spot on the skin over the head. Reiss-
ner328 also noted a similar spot. Stieda called this spot the
Scheitelfleck (parietal spot). To this spot he gave an inter-
pretation of much interest, for he believed that it marked the
situation of a peculiar, subcutaneous frontal gland directly under
the skin and this gland, therefore, became known as the frontal
subcutaneous gland of Stieda. A fine, thread-like structure led
from the skull to this gland and thus connected them. Ciaccio65
in 1867, following Stieda's lead, placed this structure among the
so-called nerve glands of Luschka. Leydig233 in 1856 considered
the organ merely as a skin gland, but Goette151 in 1873-75 studied
the epiphysis developmentally and stated that the subcutaneous
frontal gland was nothing more than the detached distal end of
the epiphysis.

The pineal region in amphibia, generally speaking, comprises
the following structures: The lamina supraneuroporica, which
is a short and thick end wall of the forebrain. The next and,
perhaps, most conspicuous element of the pineal region in am-
phibia is the massive and vascular paraphysis which, according
to certain authorities, reaches its highest development in these
forms. It has all the characteristics of a tubular gland with a
definite sinusoidal circulation and a canal which connects it with
the ventricles of the brain. The velum transversum is short

32

i i;i:i)i:i;i( K TILXKY AND LUTHER F. WARREN

and plexiform, in many forms attaining a marked vascularity.
The next structure in the pineal region is the commissura habenu-
laris, following which is a long pars intercalaris anterior. Then
fallows the epiphy-i- or the proximal portion of the pineal organ
with a marked pineal recess. There can be little doubt that
this particular form in which the pineal organ presents itself
i- the actual proximal part of other species. Following the
epiphysis is a thick pars intercalaris posterior, and finally the
posterior commissure.

Po

Npin
'

L'-V"-'-1 i-i-Lir J ly-tri-iET i 1 1 1 1 ii vrj , TJIIII_IT, j t rjirr^

Fig. 4 Schematization of the pineal region in Amphibia, according to Stud-
nicka, 1905.

/-v., lamina tcrminalis; Pf., paraphysis; I)*., dorsal sac: Ch.. commissura ha-
benularis; /'<»., pineal organ; A'/*///, IHTVUS pinealis; !•'/>., proximal portion pineal
• MM.III: '/'/).. tract us pinealis; Sch., pars intercalaris posterior; Cp., commissura
posterior; M ., midbrain.

7. The pineal region in rcptiia

In IM-osaurians and Saurians, as in Petromyzon, and some
teleosts, both the pineal and para.pin al organs make their appear-
anci-. lint the order which they hold in the lower forms is some-
what reversed here since the parapineal organ gives rise t<> an
eye-like sti'ucture called the parietal eye. This parietal eye,
h \\e\rr. is |)i-esenl only in the lower reptiles. The pineal organ,

THE PINEAL BODY 33

on the other hand, in most forms presents a less well-developed
appearance, and in many instances (in Lens a stricto) an epi-
physis cerebri alone may be observed. The parietal eye, earlier
but incorrectly called the pineal eye, is absent in many
forms even among the lower reptiles. It is undoubtedly the
homologue of the anterior epiphyseal organ or parapineal organ
of teleosts and perhaps the parapineal organ of Petromyzon.
No chapter in the morphology of the pineal organ is more
replete with interest or full of incentive to further research than
that dealing with the remarkable conditions observed in this
region of the brain in reptilia. From the observations on the
Saurians and Prosaurians have come far-reaching theories into
the phylogenesis of the vertebrates as well as many illuminating
efforts to trace the evolution of this phylum by means of the
unpaired parietal eye back to the invertebrates. Brandt40 in
1829 was first to mention the presence of the epiphysis in the
Saurian brain. Milne-Edwards107 and Duges97 both in 1829
referred to certain scales in the head of Lacerta. Neither of
these authors described the structures, but their illustrations
plainly indicate that they had perceived the area in the skull in
which the parietal eye comes to the surface. Cuvier77 and
Tiedemann395 had both observed the organ in reptiles. Leydig234
in 1872 studied the embryo of Lacerta and Anguis, giving partic-
ular attention to the parietal region of the skull. He described
a peculiar body made up of long, epithelioid, and cylindrical
cells. These cells were so arranged as to form a rim, the border
of which comprises cells of a deep black pigment. This organ
was not, as one might think, the epiphysis, for this latter struc-
ture lies distinctly above the organ described by Leydig. Ley-
dig, furthermore, mentioned a parietal foramen and a spot on
the skull indicating the position of the organ which lies beneath
it. This structure Leydig called the frontal organ, and while he
strongly suspected that it was possessed of sensory function, he
did not commit himself to such a theory at the time in which he
wrote. Strahl382 in 1884 thought that this frontal organ of
Leydig had certain relations to the epiphysis and seemed able to
demonstrate that Leydig's organ was nothing more than a

MEMOIR NO. 9

X

*. V __.

34

FREDERICK TILNEY AND LUTHER F. WARREN

detached distal portion of the epiphysis, the homologue of the
frontal gland in amphibians. The idea advanced by Strahl was
subsequently confirmed by Hoffmann186 in 1886 and again by
Beraneck21 in 1887. But it is to deGraaf155 that we are indebted
for the first demonstration that the organ of Leydig was pro-
vided with a lens and a retina and was, hence, a real visual organ.
This work of deGraaf in 1886 was almost simultaneously con-

Fig. 5 Scheraatization of the pineal region in Sphenodon, according to Stud-
nicka, 1905.

Ls., lamina terminalis; V., velum transversum; Pf., paraphysis; Ds., dorsal
sac; Ch., co.nmissura habenularis ; I'd., parapineal organ; Npar., nervus parapi-
nealis; !'<>., pineal organ; Ep., proximal portion pineal organ; T 'p., tractus pinealis;
Sch., pars intercalaris posterior; Cp., comrnissura posterior; M., inidbrain, A'/*.,
accessory parapineal organ; l\., Krrrssus pinralis.

firmed in the same year by Spencer366 who carried on a large
number of observations upon many different Saurian forms,
confirming in detail the proposition advanced by deGraaf that
the structure described by Leydig as the frontal organ contained
nol only a lens, but a definite retina. These works led up to
the later investigations on the parietal eye and also on what has
been called the third eye of vertebrates.

THE PINEAL BODY

35

The parietal eye which occurs in many forms of Lacertilia is,
on the other hand, entirely absent in Ophidians, Chelonians, and
Crocodilians. In all reptiles, with the exception of Lacertilia,
the epiphyseal complex is so rudimentary that only the proximal
portion of the pineal organ remains. Indeed, in Crocodilia even
this is said to be absent.

rrrnn

Ls.

Fig. 6 Schematization of the pineal region in Ophidia, according to Studnicka,
1905.

Ls., lamina terminalis; Pf., paraphysis; V., velum transversum; Ds., dorsal
sac; Ch., commissura habenularis; Ep., proximal portion of pineal organ (epiphy-
sis); Cp., posterior commissure.

Burckhardt45 in 1893 gave the first description of the pineal
region n the brain of Lacerta. He described a thin and flat
lamina supraneuroporica above which arose, to a considerable
height, a simple tubular paraphysis. In adult animals, as a
rule, this structure has the form of a thin-walled sac lined by
cuboidal ependymal cells. The paraphysis at first is without
vascularization, but later, by the ingrowth of blood vessels, it
becomes highly plexiform in character; yet in no instance is it
comparable to the vascularity observed in Amphibians. The
distal extremity of the paraphysis is flexed dorsally and often

3() FREDERICK TILNEY AND LUTHER F. WARREN

comes in contact with the ventrally flexed distal extremity of
the parietal eye. The velum transversum is well developed and
is plexiform in character, being highly vascular in structure.
Following the velum transversum is a dorsal sac usually, how-
ever, less conspicuous than the paraphysis and oftentimes smaller
than that organ. The commissura habenularis follows and is
in connection with two symmetrical ganglia habenulae. A pars
intercalaris anterior is not observed.

The epiphyseal complex has a different arrangement in the
several different classes of reptilia. In most Lacertilia the part
wlii cli seems to be the homologue of the parapineal organ has
become converted into a definite parietal eye with lens, retina,
and nerve of its own. The pineal organ, on the other hand, is
much reduced and appears but a remnant of the homologue of
this structure in some of the lower forms. In the orders of
reptilia, other than Lacertilia, the parapineal organ does not
develop and the pineal organ itself is reduced to a mere rudiment,
being represented wholly by the development of its proximal
portion. A short pars intercalaris posterior follows the epi-
physeal complex while a relatively large posterior commissure
forms the caudalmost structure in the roof of the interbrain.

8. The pineal region in aves

In birds, only the proximal portion of the pineal organ, the
part usually called the epiphysis or corpus pineale, develops.
It usually appears as a small circumscribed sac connected with
the roof of the interbrain or else it has a definitely glandular
structure with acini of varying size. Mihalkovicz274 in 1874-77
studied the epiphysis in Meleayris yallopavo and in this bird
called attention to the definite follicular and glandular char-
acter of the tissue. Mihalkovicz' description is the most com-
plete concerning the epiphysis in birds. Galeotti140 in 1892
added some details to Mihalkovicz' description of this struc-
ture and confirmed the opinion that it was glandular in its nature.
The pineal region in birds is compressed cephalodorsad because
of the marked development of the hemispheres and the cere-

THE PINEAL BODY

37

bellum. This region contains in more or less rudimentary form
the following structures: A paraphysis, a very simple velum
transversum, a small and compressed dorsal sac, a commissura
habenularis, an epiphysis, undoubtedly the homologue of the
proximal portion of the pineal organ with a definite pineal recess
and a pineal peduncle, a pars intercalaris posterior of varying
size depending upon the species, and a fairly well-marked pos-
terior commissure. The relation of the epiphysis to the brain
roof in birds is different from that encountered in any of the

Kl

IS

^ W .

Ch Cp ;
M

Fig. 7 Schematization of the pineal region in Aves, according to Studnicka,
1905.

Ls., lamina terminalis; Pf., paraphysis; Ds., dorsal sac; Ch., commissura
habenularis ; Ep., proximal portion of pineal organ (epiphysis); Cp., posterior
commissure; M., midbrain.

lower forms in that here the axis of the organ is at right angles
to the roof, whereas, lower in the scale the tendency has been
for the body to show a definite anterior or ventral flexion.

9. The pineal region in mammals

This region is made up as follows in the mammal : Following a
thin lamina supraneuroporica there occurs, according to Fran-
cotte129 in 1894 in the early stages of development in the human
embryo, a short tubular process which he terms the paraphysis.

38 FREDERICK TILNEY AND LUTHER F. WARREN

d'Erchia ('96) 109 found this structure only as a simple fold in
the embryo, while recently Warren ('17)417 has identified a small
but solid protuberance at the anterior extremity of the inter-
brain roof-plate in the human embryo which he believes is the
anlage of the paraphysis. This, however, soon disappears, leav-
ing no trace of its presence, although there develops in the
neighborhood of its origin certain prolongations which Warren
has described as the diencephalic prolongations. In the adult
brain of other mammalian forms no paraphysis has been ob-
served. The velum transversum, if present at all, has been
observed in the early embryonic period only and then as a simple
fold. This statement is based on the observations of d'Erchia.
The dorsal sac, because of the much-altered condition in the
mammalian brain due to the development of the corpus callosum,
has become much flattened and reduced to the level of the general
plain of the roof-plate. It has undergone further change in the
fact that it has acquired a rich vascularization and become
definitely plexiform, giving rise to the tela chorioidea superior
of human anatomy. The caudalmost portion of the dorsal sac
immediately in front of the epiphysis is elevated and pushed
back over the dorsal surface of the pineal body in such a way as
to form a thin, roofed sac whose ventral wall lies upon the dorsal
surface of the epiphysis. This is the recessus suprapinealis
described by Reicherl326 in 1859. A commissura habenularis is
the next element in the roof-plate, and this is situated in relation
with the peduncle of the epiphysis. The epiphysis in mammals
undoubtedly represents the proximal portion of the pineal organ.
The epiphysis itself is a solid, more or less conical shaped body
connected with the roof of the brain by one or more sets of
so-called peduncles. As a result of the development of the
corpus callosum, the epiphysis has gradually been brought to
assume a position which brings it into relation with the superior
colliculi of the midbrain. Situated between the epiphyseal
peduncles there is a small pineal recessus. The entire epiphysis
is located in a position much removed from the inner surface of
the skull.

THE PINEAL BODY

39

SgM^^^^

M

Fig. 8 Schematization of the pineal region in Mammals, according to Stud-
nicka, 1905.

Ds., dorsal sac; Ch., commissura habenularis; R., recessus pinealis; Ep., proxi-
mal portion of the pineal organ (epiphysis) ; Cp., commissura posterior; M.,
midbrain.

In the light of the phyletic review just given concerning the
structures constituting the pineal region, it becomes clear that
any satisfactory consideration of the epiphyseal complex must
take into account the characters of the parapineal organ as
well as those of the pineal organ. It seems advantageous to
discuss the comparative embryology of these two parts and
then to consider the phyletic characteristics of each of them
separately. In this way the modifications of each organ may be
followed consecutively from one order to the next.

5. THE COMPARATIVE EMBRYOLOGY OF THE EPIPHYSEAL COMPLEX
1. The development of the epiphyseal complex in cydostomes

According to Studnicka ('93) 384 and other observers, a small
evagination in the caudal portion of the roof-plate of the inter-
brain makes its appearance as a simple and single protrusion
from the roof. This is the pineal organ. There can be no
question but that it develops first of the two elements in the
epiphyseal complex in these forms. The anlage of the pineal
organ increases greatly in size so as to present an end-sac or

40

FREDERICK TILNEY AND LUTHER F. "WARREN

end-vesicle, a stalk and a proximal portion connecting it with a
ventricle of the brain. At first, the end-vesicle contains a cavity
which gradually decreases in size so that the lumen becomes
little more than a cleft or entirely disappears. The stalk also
contains a large canal which is gradually reduced in size. The
ventral wall of the end-sac becomes converted into a structure
resembling the retina, in which many nerve fibers are to be
observed. In the dorsal wall of the sac nerve fibers running
from the end-vesicle soon make their appearance. These fibers
come into relation with the posterior commissure and constitute
what is known as the nervus pinealis. The proximal portion is
represented by a very short, dilated structure which contains
the recessus pinealis.

Po

Fig. 0 Anlage of the epiphyseal co nplex in an o.nbryo of Petromyzon, accord-
ing to KupiTcr, l'.K)4.

Ls., lamina terminalis; I'i>., paraphysis; Ch., commissura habenularis; Po.,
pineal organ; ('/>., commissura posterior.

At a considerably later embryonic period the anlage of Stud-
nicka's parapineal organ first makes its appearance. It develops
entirely independent of the anlage of the pineal organ. The
evagination which first makes its appearance as the parapineal
anlage shortly becomes greatly elongated to form a tubular
prolongation from the roof of the brain. The terminal portion of
this tubular evaginatioD becomes dilated to form, as in the case of
the pineal organ, an end-vesicle, while a slender stalk connects the
latter with the brain roof. The ventral wall of the end-sac of
the parapineal organ, as in the case of the pine:il organ, develops

THE PINEAL BODY 41

a pigmented structure and in it appears a number of nerve fibers.
In the later embryonic stages the stalk connecting the end-
vesicle of the parapineal organ with the brain attenuates, loses
its lumen, and shows the presence in it of numerous nerve fibers
which may be traced to the commissura habenularis. The rapid
elongation of the stalk in the parapineal and pineal organs as
development advances causes these structures to be moved
further away from the roof-plate and near the under surface of
the skull. The general direction of this growth is cephalodorsad.
Gaskell145 showed in Ammoccetes a right and left pineal eye.
It is his opinion that the pineal and parapineal organs represent
a paired set of eyes. Their relation to each other, in which the
parapineal organ occupies the more cephalic position, was deter-
mined, according to Gaskell, by the exigencies of development.
In reality, however, he believes that the ancestors of vertebrates
must have possessed a pair of median eyes.

Dendy86 also observed in cyclostomes a double evagination
from the roof-plate giving rise to the epiphyseal complex. It is
his opinion that the right evagination produces the parietal eye
while the left becomes the parapineal organ, and Dendy, like
Gaskell, maintains that the ancestors of the vertebrates must
have been possessed of a pair of parietal eyes which may have
been serially homologous with the ordinary vertebrate eyes.
Scott ('81)349 and Dohrn (75) 95 both showed that the epiphyseal
complex developed as evaginations from the roof of the in-
terbrain. These observations were essentially confirmed by
Shipley ('87),354 Owsiannikow ('88),295 Studnicka ('93), 384 and
Kupffer C94).224

2. The development of the epiphyseal complex in selachians

Balfour10 in 1878, in Acanthias, d'Erchia109 in 1896, in Pris-
tiurus, and Minot277 in 1902, also in Pristiurus, investigated the
development of the epiphyseal complex. According to all of
these authors, a single evagination arises in the roof-plate im-
mediately in front of what is later to be the posterior commissure.
This evagination gives rise to the pineal organ inasmuch as the
parapineal organ does not appear in selachians. From its

42 FREDERICK TILXEV AND LUTHER F. WARRKX

inception this ovagination is a small, cordiform enlargement
which rests at first directly upon the ectoderm of the upper
surface of the head. The gradual lengthening of the tubular
pineal organ, which is similar to what occurs in Petromyzon, is
in the main duo to the fact that a very large amount of mesen-
chyme makes its appearance between the roof of the brain and
the under surface of the skull. In this way the end-vesicle of
the pineal organ maintains its relative position to the ectoderm
and thus always remains near the surface of the skin. In many
instances the end-vesicle comes to lie in a large foramen of the
skull, that is, the parietal foramen which makes its appearance
at a later stage of development.

Considering the embryological development of the pineal
region in selachians, Locy244 holds that two pairs of accessory
optic vesicles are preserved in the cephalic plate of Elasmo-
branchs, his particular reference being to Squnlus acanthias.
These accessory optic vesicles together with the primary optic
vesicles give rise to two pairs of rudimentary eyes. The epi-
physis is, therefore, of double origin, forming a united pair of
accessory optic vesicles, and since the latter are homologous
with the lateral eyes, the epiphysis itself must be homologous
with these eyes also. His contention that the pineal outgrowths
arise from two pairs of vesicles that are homologous with those
giving origin to the lateral eyes has not been altogether sustained
by other observers. Locy is also of the opinion that it is highly
probable that the enlarged distal end of the epiphysis inSqi«ili<*
is homologous with the pineal eye in those forms in which it is
differentiated. Cloetteir'2 in 1875 expressed the opinion that the
opiphysis in selachians was a product of differentiation at the
point of union between the brain and the epidermis. He com-
pares the pineal organ to the pore which persists for a long time
in the embryo of Ampliioxux and leads into the encephalic cavi-
ties. Khlers'"s in 1878 confirmed the findings of Balfour in
Rfiiti clnratii and Arti nlliiux rul<i<irfx. An interesting observa-
tion in this connection is the finding by Cat tie'111 of the pineal
organ in T»ri>< <!<> rrnirtn<,r<il<i. Cattie observed the organ in the
embryonic state in this form. The importance of this observa-

THE PINEAL BODY

tion lies in the fact that Studnicka391 says that the organ is absent
in Torpedo marmorata and d'Erchia109 says that in Torpedo
ocellata there is no pineal organ.

1 ml

j '

'Cr

Fig. 10 The epiphyseal complex in an 86 mm. embryo of Acanthias vulgaris,
according to Minot, 1901.

Hm., hemisphere; P/., paraphysis, V., velum transversum ; Ds., dorsal sac:
Ch., commissura habenularis; R., recessus pinealis; Po., pineal organ; Cp.,com-
missura posterior; M., midbrain.

One of the authors, Tilney ('15), 396 studying the interbrain in
Mustelus laevis, illustrated the development of the pineal organ
in reconstruction models through a number of stages. The
anlage of the epiphyseal complex in Mustelus makes its first
appearance in the 9 mm. embryo as a single evagination from the
roof-plate. It is a prominent element in this region for some

44

FREDERICK TILXEV A XI) LUTHER F. WARREX

tune before the appearance of the paraphysis. In the embryo
of an 11 nun. Miixtclus the evagination appears rising well
above the general plane of the roof.

It is bounded by a thin cephalic and a thicker cauda1 wall.
A recess of considerable depth extends into it; it retains com-

29

Fiu. 11 Mesial vie\\- of forebrain reconstruction of 11 nun. Mustelus embryo.
X 100. The unshaded area shows the cut surfaces of the reconstruction. Ac-
cording to Tilney. 1!H.">.

1, cliiiism : 7. epiphysis; IN, infundibular evagination; 21. midbrain; 2.~>, mam-
in ill a ry region : _".», optic e vaginal ion; 36, post-in fund! I )iilar (-vaginal ion ; -H, tel-
encephalon; L5, tuberculum postero-superius; 46, tubercle of the Boor of Schulte

inimical ion \vilh tin- third ventricle. The inception of the velum
transversum may be discerned, but no paraphysis is pi'esent.
rl'he changes observed in passing from the 1 1 mm. to the 'JO mm.
embryo consist in the now definite ap|>"arance of the velum
transversum and the elongation of the pineal organ.

THE PINEAL BODY

45

3332

Fig. 12 Mesial view of forebrain reconstruction of 20 mm. Mustelus. X 75.
The unshaded area shows the cut surfaces of the reconstruction. According to
Tilney, 1915.

2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 18, infundibular
evagination; 24, midbrain; 25, mammillary region; 32, post-chiasmatic eminence;
33, post-chiasmatic recess; 36, post-infundibular eminence; 41, supra-optic crest;
42, supra-optic recess; 44, telencephalon; 45, tuberculum postero-superius; 46,
tubercle of the floor of Schulte; 47, velum transversum.

In the latter there is a slight tendency for the evagination to
become expanded as if to form an end-vesicle. It is, therefore,
possible at this time to recognize a stalk and an end-sac.
Neither in this stage nor in any subsequent period of develop-
ment is there evidence of a parapineal organ. The paraphysis

46

FREDERICK TILXEY AND LUTHER F. WARREN

has not yet made its appearance. In the 50 mm. embryo, how-
ever, the paraphyseal milage is present and the pineal organ
has become still further elongated.

The tendency toward expansion of the dista extremity is not
as marked as in the 20 mm. embryo. The pineal organ still
contains a lumen throughout its entire extent. The expansion
of the pineal organ to form an end-sac is again pronounced at
the stage of 70 mm.

44
39

32

13

Fig. 13 Mesial view of forebrain reconstruction of 50 mm. Mustelus. X 50.
The unshaded area shows the cut surfaces of the reconstruction. According to
Tilney, 1915.

2, chiasmatic process; '•',. cerebellum ; t. diiasm; 7, epiphysis; 13, infundibular
process; -I, midbrain; '2~>, iiiaiiimillary region; 3:2, post-chiasmatic eminence
(lobus-inf erior) J .'53, post-chiasmatic recess (recess of inferior lobe); 3(1, post-
infundibular evaginat ion ; 3(.l, paraphysis; 10, recess of infundibular process; 11.
supra -opt ic crest ; I'J. supra-opt ic recess : 1 I. telencephalon ; 17, velum trans versum.

THE PINEAL BODY

47

The sac is hollow and in communication with the ventricle by
means of a slender, hollow stalk. A proximal portion may now
be distinguished so that all three elements of the pineal organ are
present. The habenular ganglion is recognizable at this stage
as a marked thickening in the roof-plate cephalad of the pineal
organ. The paraphysis and velum have increased in promi-

24

42

Fig. 14 Mesial view of forebrain reconstruction of 70 mm. Mustelus. X 50.
The unshaded area shows the cut surfaces of the reconstruction. According to
Tilney, 1915

2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 18, infundibular
evagination; 24, midbrain; 26, mammillary recess; 27, mammillary body (poste-
rior lobe) ; 32, post-chiasmatic eminence (inferior lobe) ; 33, post-chiasmatic
recess (reces-s of inferior lobe) : 35, post-infundibular recess; 36, post-infundibular
eminence; 39. paraphysis; 40, recess of infundibular process; 41, supra-optic crest;
42, supra-optic recess; 44, telencephalon; 47, velum transversum.

nence. The brains of the 100 mm. and 300 mm. Mustelus
approximate the adult conditions shown in figures 15, 16 and 17.
Here, with one exception, i.e., the parapineal organ, all of the
elements in the pineal region may be identified, including the
two parts of the paraphyseal arch, the velum transversum, a
short dorsal sac, a massive habenular commissure and habenular

4S

FREDERICK TILNEY AND LUTHER F. WARREN

ganglion, a pineal organ consisting of an end- vesicle, stalk and
proximal portion, and finally the posterior commissure.

36 27 3

39

Fiji. 1") .Mesial view <if brain reconstruction of 100 mm. Mustelus. X 25.
The unshaded area shows the cut surfaces of the reconstruction. According
to Tilney, 1915.

2, chiasmatic process; 3, cerebellum; 4, chiasin; 7, epiphysis; 13, infundibular
process; 14, infundibular process, saccular surface; 15, infundibular process, pitui-
tary surface; 20, lamina t enniiialis ; 1M, midbrain; 27, mammillary body (post-
erior lobe); 32, post-chiasmatic eminence (lobus inferior); 33, post-chiasmatic
recess (recess of inferior lobe); 36, post-infundibular evaluation; 3!), paraphysis;
40, recess of infundibular process; 41, supra-optic crest; 42, supra-optic recess;
44, telenccphalon; 47, velum transversum.

3. The development of the epiphyseal complex in ganoids

Kupffer223 1893 gave the first detailed description of the develop-
ment of the epiphyseal complex in Acipenser. The anlage of the
organ he describes as a small single evagination which later
becomes a stalk with an (Mid-vesicle. Kupffer could find
nothing of the anterior or parapineal organ. Owsiannikow
('88)295 gave a description according to which inthe three- or
four-weeks old embryo of Acificnxcr just in front of the pineal
organ there appears a small, round or cordifonn structure.
llillls" in 1X1M described a small rudimenl of the anterior or
parapineal organ in Aniia calru. In the 10 mm. embryo this
bodv was ovoid in form and situated immediately in front and

THE PINEAL BODY

49

to the left of the pineal organ. It was connected with the roof-
plate by means of a thin stalk. In the 13 mm. embryo this
organ has come to lie above the commissura habenularis and
still later it is consolidated into a mass of cells lying to the left
beneath the now markedly developed and ventrally flexed
pineal organ. Eycleshymer and Davis113 in 1897 confirmed the
observation of Hill and noted that the anterior or parapineal

44

13

15

10

32 33

Fig. 16 Mesial view of brain reconstruction of 300 mm. Mustelus. X 25.
The unshaded area shows the cut surfaces of the reconstruction. According to
Tilney, 1915.

2, chiasmatic process; 3, cerebellum; 4, chiasm; 7, epiphysis; 10, hypophyseal
recess; 13, infundibular process; 14, infundibular process, saccular surface; 15,
infundibular process, pituitary surface; 24, midbrain; 27, mammillary body (pos-
terior lobe); 32, post-chiasmatic eminence (inferior lobe); 33, post-chiasmatic
recess (recess of inferior lobe); 36, post-infundibular evagination; 39, paraphysis;
40, recess of the infundibular process; 41, supra-optic crest; 42, supra-optic re-
cess; 44, telencephalon; 47. velum transversum.

organ possessed a lumen late in the course of development.
Both the anterior and posterior pineal organs in the embryonic
stages have nerve fibers which connect them with the habenular
commissure. The earlier works upon this region in ganoids were
done by Salensky341 in 1881 and Balfour and Parker12 in 1882
(fig. 18).

MEMOIR NO. 9

50 FREDERICK TILNEY AND LUTHER F. WARREN

4. The development of the epiphyseal complex in teleosts

Rabl-Riickhard818 in 1882 gave the first explanation of the
development of the epiphyseal complex in teleosts. Hoffmann185
in 1884 also described the ontogenesis of the pineal organ in

14

10

33

21

Fig. 17 Mesial view of brain reconstruction in adult Mustclus laevis. X 25.
The unshaded area shows the cut surfaces of the reconstruction. According to
Tilney, 1915.

'2, chiasmatic process; 3, cerebellum; 4, chiasm; 6, divcrticular sacci vasculosi;
7, epiphysis; 10, hypophyseal recess; 12, infundibular canal ; 14, infundibular proc-
ess, saccular surface; ir>. infundibular process, pituitary surface; 20, lamina ter-
ininalis; 21, median chiasmatic groove; 24, midbrain; 2(5, manunillary recess (re-
• IBS <>f posterior lobe) ; 27, mammillary body (posterior lobe) ; 32, post-ehiasmatic
eminence (inferior lobe); 33, post-chiasmatic recess (recess of inferior lobe) ; 34,
post-infundibular eminence; 35, post-infundibular recess; 39, paraphysis; 42,
supra-optic recess; 14, telencephalon; 47, velum transversum.

teleosts. Both authors employed the same forms, namely,
Sal mo fario and Sfdmo salar. According to their descriptions,
the anlage begins as a small evaginat ion which gradually elon-
gates ;ui(l grows more and more narrow. It has produced a
proximal portion, a stalk and an end-vesicle which lie just
beneath the inner surface of the skull in the frontal region.

THE PINEAL BODY

51

Still later many small diverticula develop in the walls of the
end-vesicle which become unusually large. A feature of the
description of the development given by these authors is the
absence of any anterior or parapineal element in the epiphyseal
complex, for this organ, according to their observations, does

M

Cp R Ch Ds

Pf Ls

Rn

Fig. 18 The epiphyseal complex in a four months old embryo of Acipenser
sturio, according to Kupffer, 1893.

Ls., lamina terminalis; P/., paraphysis; V., velum transversum; Ds., dorsal
sac; Ch., commissura habenularis; R., recessus pinealis and pineal organ; Cp.,
commissura posterior; M., midbrain.

not even make its appearance in anlage. Holt ('91) 189 described
the development of the epiphyseal complex in Clupea harengus.
In this form the organ began as a solid sprout and later devel-
oped a lumen. The walls of the end-vesicle were eventually
thrown into a number of diverticula. Mclntosh and Prince254
in 1891 confirmed the findings of Hoffmann and Rabl-Rtickhard.
Hill's179 observation in 1891 is of unusual importance, for this
observer, working upon Coregonus albus and later180 in 1894 on
Salmo catostomus teres, Stizosthetium vitreum, and Liponus
callidus, found what he took to be the anlage of the anterior or
parapineal element just as he had found this element in Amia

52 FREDERICK TILNEY A XI) LUTHER F. WARREN

calm. In the embryo of S<tl///<> fotitinali*, IIillIMJ found the
unlade of tlie ej)i])hyseal complex to be a double evaluation
which communicated with the third ventricle by means of a
common canal. Of the two sacs thus formed the posterior was
much the larger. This, the anlage of the pineal organ, was
situated immediately in front of the posterior commissure and
in the mid-line, while the anterior evagination was close to the
left as if both sacs were related to the roof-plate by a common
stalk and later the anterior one was detached from the connec-
tion. Hill concluded that there are two epiphyseal outgrowths
from the roof in teleosts of which the more anterior vesicle, both
in teleosts and in Aniia, is homologous with the parietal eye of

PC Pp

Fig. 19 Anlage of the epiphyseal complex in a 37-days old embryo of Salmo
fontinalis, according to Hill, 1894.

Pp., parapineal organ; Pt>., pineal organ.

Lacertilia. He thinks it probable that the two vesicles in their
primitive position were side by side and believes it likely that
the anterior vesicle is the homologue of the parapineal organ in
Pelromyzon. Hill also found this condition in embryos as well
as in a two-year-old salmon.

Dendy86 maintained that the double evagination in the epi-
physeal anlage occurs in Amia as well as teleosts. Of these two
vesicles the right gives rise to the epiphysis while the left sepa-
rates from the brain a.nd degenerates. Cattie,60 examining the
adult condition in plagiostomes, ganoids, and teleosts, came to a
conclusion similar to the hypotheses of (loette11- and Van Wijhe-107
that the pineal body was derived as the final product of closure
at the anterior neuropore where the ectoderm of the epidermis

THE PINEAL BODY 53

and of the nerve tube remained longest in continuity. Van
Wijhe407 in 1884 expressed the belief that the epiphysis in teleosts
was a remnant of the anterior neuropore, but later he gave up
this idea. Rabl-Riickhard318 in 1882, studying the epiphysis in
embryos of bony fish, summarized the process of development
from the comparative standpoint in the following words:

Allein wahrend diese unter Mitwirkung cles sich zur Linse einstiil-
penden Ectoderms und des Mesoderms complicirte Veranderungen ein-
gehen, die schliesslich zur Entwickelung des hochst entwickelten Sin-
nesorganes, des Auges, fiihren, sehen wier an der Zirbeldriise trotz der
giinstigen Lage ihres distalen Endes dicht unter dem Ectoderm nichts
dergleichen. Mann denke sich eine ahnliche Wucherung und ihre Folgen,
wie an dem die Augenblasen bodeckenden Ectoderm, das Auftreten von
Pigment im sich betheiligenden Mesoderm, und nichts steht der Vor-
stellung im Wege, dass sich aus der Zirbel ein dem Auge dhnliches, un-
paares Sinnesorgan entwickelt. Interessant ist, dass diese Gegend in
einem bestimmten Embryonal-stadium bei Reptilien (Lacerta Anguis)
eine ahnliche Entwickelung wenigstens andeutungsweise zeigt, und dass
hier am Scheitelbeine des fertigen Thieres sich ein Kreisrundes Loch
befindet. Bekanntlich hat schon Leydig diesen Refund eingehend
erortert und die Vermutlmng ausgesprochen, dass es sich vielleicht um
ein "Organ des 6 Shines" handelt.

And again in 1886:

Das Schadeldach der riesigen fossilen Enaliosaurier cles Lais des Ich-
thyosaurus und Plesiosaurus besitzt ein unpaares Loch, welches seiner
Lage nach mit dem Loch in Scheitelbein der Saurier iibereinztistimmen
scheint. Vielleicht lag auch hier das viel entwickeltere Zirbelorgan
mit seineni distalen Endtheil zu Tage, und man konnte sich vorstellen
das seine Leistung nicht sowohl die eines Sehorgan als die eines Organs
des Warmesinnes war, dazu bestimmt, seine Trager vor der zu inten-
siven Einwirkung der trophischen Sonnenstrahlen zu warnen, wenn sie
in trager Ruh, nach Art ihrer noch lebenden Vettern der Crocodile,
sich am Strande und auf den Sandbanken der Laisse sonnten.

5. The development of the epiphyseal complex in amphibia

In Urodela, deGraaf ('86) 155 found that the embryo of Triton
had the anlage of its epiphyseal complex in a simple and single
saccular evagination from the roof of the interbrain. These
observations were confirmed upon Amblyswma embryos by
Orr286 in 1899, by His183 in 1892 and by Eycleshymer112 in 1892.
Beraneck24 in 1893, working upon Salamandra embryos, observed

54 FREDERICK TILXEY AM) LUTHER F. WARREN

the anlage of the epiphyseal complex to ho a hollow sac which
laid- became saccular and cylindrical, containing throughout its
entire extent a lumen which still opened into the third ventricle.
In this form it was possihle to identify an end-vesicle, a stalk, and
a proximal portion. These conditions were obtained at a period
of 1'J mm. embryo, but at the stage of the 18-mm. embryo the
lumen in the stalk was obliterated. In this manner the stalk of
the pineal organ became gradually reduced in size until finally
it presented itself as a mere strand connecting an almost com-
pletely isolated end- vesicle lying beneath the skull with a well-
marked proximal portion in communication with the third
ventricle. In Salamandra the paraphysis develops very early
and assumes extensive proportions resembling the chorioid
plexus. The embryological conditions in A nurd are, according
to most descriptions, quite similar to those in Urodela. Goette152
in 1873-75 observed in the anlage of the pineal organ the remains
of the anterior neuropore. This error, as has already been
stated, was pointed out by Hoffmann1815 in 1886 and Heckscher1690
in 1890. In Rana, Beraneck-4 described the first appearance of
the. anlage of the epiphyseal complex as a small, ellipsoid evagi-
nation which later becomes cylindrical. This evagination con-
tains a small lumen. Elongation gradually occurs so that an
end- vesicle, a stalk, and a proximal portion are formed. In the
later stages of development the stalk undergoes attenuation
until it is reduced to a mere strand containing, it is thought,
some nerve fibers. This leaves the end-vesicle situated at a
point remote from the brain beneath the skull, while the proximal
portion is a large and somewhat spacious evagination still main-
taining a wide connection with the third ventricle. The nearly
isolated end-vesicle Beranock calls the corpus < /i/tiieliale. This
body lies beneath the skin over the head and has the appearance
of a gland-like structure. In embryos of Bufo, Beraneck-1
observed close to the commissiira habonularis a small prominence
which early disappears; this he identified as the anlage of a
transitory parapineal organ. For the most part, however,
observers ha,ve found that a single evagination in the roof-plate
marks the milage of the epiphyseal complex 'fig. -0).

THE PINEAL BODY

55

Eycleshymer,112 in attempting to explain the unpaired origin
of the epiphysis in Amblystoma, maintained that in the phylo-
genetic period when the lateral eyes became implicated by the
closing of the neural fold, a median eye would arise and thus
become most highly functional during the time when the lateral
eyes were little, if at all, functional. Cameron,50 working with
the embryos of Rana, Bufo, and Triton, concluded that the

Fig. 20 Anlage of the epiphyseal complex in a 13 mm. embryo of Salamandra
maculata, according to Kupffer, 1893.

Ls., lamina terminalis; P/., paraphysis; V., velum transversum ; Ds., dorsal'
sac; Ch., commissura habenularis ; Po., pineal organ; Sch., pars intercalaris pos-
terior; Cp., commissura posterior; M, midbrain.

epiphysis in amphibia arises as two primary outgrowths from
the roof of the forebrain (fig. 21).

These are placed one on either side of the mesial plane. The
outgrowth situated to the right of the middle line disappears at
an early age by blending with the left outgrowth. The latter
shows most active growth so that the epiphyseal opening becomes
situated to the left of the mesial plane. The left outgrowth,

56

FREDERICK TILNKV AXI) LUTHER F. WARREN

however, is the more important of the two in amphibia. Cam-
eron believes that there is evidence of a bilateral origin to be
found in the later stages of amphibian development. The
portion of the anlage in connection with the superior commissure
corresponds to the parietal eye of Sphenodon while the remainder
corresponds to the epiphyseal stalk. From this evidence in
amphibia he is inclined to agree with Dendy86 that the ancestors
of vertebrates must have possessed a pair of parietal eyes (figs.
22 and 23).

Fig. 21 Anlagc of the epiphyseal complex in an embryo of Triton cristatus,
according to dodraaf, 1886.

('It , commissura habonularis; If., recossus and pineal organ; Cp., commissura
posterior; M ., midbrain; Epid., epidermis; Cor., corium.

6. The development of the epiphyseal complex in reptilia

The fact that in Prosanrnmx and Saurians a well deve'oped
eye is found in many fcrms has been the cause of much dis-
cussion ;is 1o the embryolgical process by means of which this
structure is differentiated from the epiphyseal complex. Accord-
ing to the older view, the p;tri<>tal eye arose, as in the case of the
isolated end-vesicle of amphibia, by a process of constriction
from the terminal portion of the pineal organ. Subsequently
the view was advanced that instead of a process of constriction

THE PINEAL BODY

57

it was rather a subdivision of a single evagination from the roof-
plate which gave rise to the parietal eye; more recently, however,
the opinion has been expressed by several observers, that the
parietal eye owes its existence to an anlage quite independent
from that of the pineal organ and situated anterior to the latter
in its point of development from the roof-plate of the inter-
brain. The fact that the parietal eye was not the constricted
end of the epiphysis, but was independently connected by

Fig. 22 Anlage of the epiphyseal complex in an 11 mm larva of Bufo vulgaris
according to Beraneck, 1893.

Po., pineal organ (end-vesicle); Ep., proximal portion.

means of a nerve of its own to the roof of the brain, was shown
conclusively 'by Strahl and Martin383 as well as Beraneck,23 who
was first to call attention to the nerve fibers connecting the
parietal eye with the brain, namely, the parietal nerve. Having
thus dispensed with the idea that the parietal eye was merely a
constricted portion of the end of the epiphysis proper, it re-
mained for subsequent investigation to demonstrate the actual
process by means of which the parietal eye arose. Advocating
the view that the anlage of the epiphyseal complex in Reptilia,
and particularly in the Saurian and Prosaurian forms, is an
evagination subdivided into an anterior and a posterior compart-

• )S FREDERICK TILXEY AXD LUTHER F. WARRKX

ment, there has been assembled a formidable array of evidence.
Hoffmann, lv; from his observations on Lacertd ay Hi*. Strahl and
Martin. ;v; in Ati<inix and Ldccrta riripara, Francotte,1-7 on
I.di-trid riiifxird, Klinckowstroem.-"7 in lyinunt. McKay,'--'5 in
Grammatophora mnric<tl>i. and Schauinsland,848 in *S
all advocate this view (fig. '24 .

Fig. 2:i Anlage of the epiphyseal complex in a 12 nun. larva of Bufo vulgaris
according to BcTancck, Is'.C!.

/'"., pineal organ; E/>.. proximal portion.

Beraneck,23 on the other hand, in his well-known work upon
the parietal eye and the morphology of the third eye of verte-
brates, concludes that the parietal eye should not be considered
as a simple diverticulum of the pineal gland. In Luccrld and
Anguis it constitutes an independent organ which develops from
the thalainencephalon as the epiphysis, but develops parallel to
the latter not dependent upon it. The parietal eye is attached
by a neural fasciculus which is transitory and not in any sense
derived from the epiphysis (fig. 2">).

THE PIXEAL BODY 59

It is part of the small mass of cells situated between the base
of the pineal gland and the first fold of the chorioid plexus. The
unpaired eye is an evagination of the dorsal wall of the inter-
brain and constitutes an optic vesicle. The separation which
sometimes occurs between the crystalline and retina of this
vesicle is ordinarily unilateral, rarely bilateral. It appears
relatively late in embryonic development and should not be con-
sidered a proof of the duality of origin of the parietal organ as
Beard18 has considered it. The unpaired eye does not occur in
chordates nor does it have its homologue in the other branches
of the metazoa. Sometimes it has its physiological analogue in
the median eye of Crustaceans. It is an ancestral organ which
was atrophied in the majority of extant forms of the different

Fig. 24 Two successive stages in the development of the epiphyseal complex
in Lacerta vivipara, according to Francotte, 1896.

Pa., parapineal organ; Po., pineal organ; M., midbrain.

branches of the chordate phylum. The primitive optic vesicle is
still recognizable in cyclostomes and Saurians ; it is rudimentary
in teleosts and amphibians, but appears to be absent in sela-
chians. On the other hand, the epiphysis in these latter forms
is very long and broadened at its distal extremity without form-
ing an optic vesicle. The epiphysis is also derived from an
evagination of the interbrain roof. It does not represent the
optic pedicle of the parietal eye. It is an organ sui generis
whose function is still unknown. It reveals no marked sensory
characteristics even in selachians where it is markedly devel-
oped. It appears in the entire series of vertebrates and is an
ancestral organ. The paired eye and epiphysis appertain to the
interbrain while the paraphysis is part of the endbrain. This

60

FUKDKKK K TILXK'i AND LUTHEB F. WARRKX

paraphysis shows no features of sensory function. Of these
three encephalic divert icula from the roof-plate in Saurians,
the parietal eye alone seems to have had ancestral sensory
function (fig. 26).

In a later communication, combating the contention of Klinck-
owstroem207 to the effect that the evolutional process observed
in An<iuis is normal and more primitive while that in Lacerta
is a simple modification of this primitive form, Beraneck25 pro-

Fig '_'."> 'I'lic epiphyseal complex in a 27 nun. embryo of Annuls fragilis, ac-
cording to Beranerk, 1X92.

/'/., paraphysis; I'., velum transversum; D.s., dorsal sac; Ch., commissura ha-
liennlaris; \/>ur.. ncrvus parapinealis; I'd., ])arapiiH'al organ; H/>., pineal organ;
Sch., pars intercalaria posterior; ('/>., conin.issura. posterior.

posed this (juestion, "If in Anguis the parietal eye is only a
differentiation of the distal extremity of the epiphysis, how in
La«'r,(t does this visual organ develop parallel to the epiphysis
and not dependent upon it?" Beraneck maintains thai Klinc-
kowstroem escapes the difficulty proposed by this question in
claiming thai the pineal eye of lynuim and f.<iccrl<i upon the
one hand and Ainjnis upon the other take origin from different
parts of the epiphyseal evaginal ion. B-.'raneek formulates the
hypothesis that the parietal eye and epiphysis represent in

THE PINEAL BODY

61

Lacerta two distinct evaginations of the thalamencephalic roof.
If they appear to be different in Iguana and Anguis that is due to
secondary modifications of this region. The evolution of the
parietal eye in Iguana is intermediate between the conditions
observed in Lacerta and Anguis. In his conclusion, Beraneck
emphasizes his belief that the embryonic facts contradict the

Xpar

Fig. 26 Frontal section showing epiphyseal complex in a 26-day old Iguana
tuberculata, according to Klinckowstroem, 1894.

P/., paraphysis; Ds., dorsal sac; Npar., nervus parapinealis; Ep., proximal
portion of pineal organ; Ch , commissura habenularis; M., midbrain

epiphyseal origin of the parietal eye in Saurians and confirm
the hypothesis of its embryonic individuality. Leydig238 in
1891 confirmed the view of Beraneck in Lacerta agilis. Dendy86
also states that the parietal eye and what he calls the parietal
stalk arise from two distinct evaginations in the roof-plate of
the interbrain. By parietal stalk, Dendy refers to the portion
of the epiphyseal complex here referred to as the pineal organ.

-

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27

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B '3

.• ' '//•'

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u , j

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'- i

'/Hi

C/L

•M

28
82

THE PINEAL BODY

63

The development of the epiphyseal complex in Ophidia, Chelonia,
and Crocodilia. The embryonic description which holds good
for the more primitive forms of reptiles must be much modified
in dealing with the more highly organized and modern forms of
this class. Hoffmann186 showed that in these reptiles the anlage
of the epiphyseal complex is laid down as a single evagination

Fig. 29 The epiphyseal complex in Tropidonotus natrix, according to Stud-
nicka, 1893.

Pf., paraphysis; Ds., dorsal sac; Ch.. commissura habenularis; Ep., proximal
portion of pineal organ; R., recessus pinealis. Cp., commissura posterior; M.,
midbrain.

from the roof-plate immediately anterior to the posterior com-
missure. This hollow evagination is ultimately transformed
into a solid body. Such a transformation has been shown by
Leydig240 and Studnicka389 in Tropidonotus (figs. 29 and 30).

Fig. 27 The epiphyseal complex in a 31 mm. embryo of Gehyra oceanica, ac-
cording to Stemmler, 1900.

Pf., paraphysis; V., velum transversum; Ds., dorsal sac; Ch., commissura
habenularis; Ep., pineal organ; Cp., posterior commissure; M., midbrain.

Fig. 28 The epiphyseal complex in a 33 mm. embryo of Platydactylus muralis,
according to Melchers, 1899.

Pf., paraphysis; Ds., dorsal sac; Ch., commissura habenularis; Ep., pineal
organ; Sch., pars intercalaris posterior; M, midbrain.

04 FREDERICK TILXEY AND LUTHER F. WARREN'

The cells constituting this solid organ arrange themselves
more or less in alveolar or aciniform cell groups and the whole
body ultimately becomes attached to the roof-plate by means of
a thin stalk or peduncle. No evidence of an anterior evagina-
tion representing the parapineal element has been observed nor
is there any evidence to show that any effort toward the devel-
opment of the parietal eye in Ophidia, Chelonia, or Crocodilia

Fig. 30 The epiphyseal complex in an older Tropidonotus embryo, according
to Leydig, 1897.

Pf., Paraphysis; Ds., dorsal sac; Ch., commissura habenularis; E/> ., proximal
portion of pineal gland.

is present. In fact, in the latter forms, namely, Crocodilia, the
entire epiphyseal complex is said to be wanting and no evidence
of its development occurs at any time during ontogenesis 'figs.
31 and 32).

One of the authors, studying the development of theepiphysis
in turtles, reconstructed the forebrain of 7TWr/.s.sm7/r///.s- cdrclxi
in several stages. The conditions in the 3()mm. embryo are
shown in figure 33. Here the pineal region consists of a well-

Ep

31

Hm

Fig. 31 The epiphyseal complex in an old embryo of Chelydra serpentina,
according to Humphrey, 1894.

Pf., paraphysis; V., velum transversum; Ds., dorsal sac; Ep., pineal organ; Cp.,
posterior commissure.

Fig. 32 The pineal region in an old embryo of Caiman niger, according to
Voeltzkow, 1903.

Hm., hemisphere; Pf., paraphysis; Ds., dorsal sac; Ch., commissura habenu-
laris; M, midbrain.

65

MEMOIR NO. 9

66

KHKDKHICK TIIA'KV AND U'THKR F. WAHRKX

marked paraphyseal evagination, a velum trans versum, a dorsal
sac, a commissTira habenularis, and a single thick-walled anlage of
the pineal body whose apex is directed cephalad. The most
caudal structure in the pineal region is the posterior commissure.

D.s

Pf

l'"\£. '•>'•'• Keconst met inn MI'. -i :!() mm. embryo of Thalassoc-liclys curctta.
7,x.. l:iinin:i tci'iiiinalis ; /'/'., parajiliysis; I'., velum t raiisvcrsum ; Ds., dorsal
sac; f'ti., CMniiinissiira lialicnularis ; !'<>., cpiphysis; Cp., posterior commissure; A'..

Kat like pocket

THE PINEAL BODY

67

'. The development of the epiphyseal complex in aves

In birds, the anlage of the epiphyseal complex makes its first
appearance as a simple and single evagination. This was first
observed and described by Reissner329 in 1851 and called by
Reichert326 in 1859 the recessus pinealis. Lieberkiihn242 in 1871
identified this evagination in birds as the anlage of the epiphysis.

In many instances the presence of a double evagination of
the roof-plate has been reported in the anlage of the epiphysis
in birds. Saint Remy340 in 1897 found on either side of the still
unclosed neural tube a small evagination in the region of the

Fig. 34 The epiphyseal complex in an 8-day embryo of Anas domesticata,
according to Hechscher, 1890.

epiphyseal anlage. This observation was made upon Gallus,
but Parker301 in 1892, in Apieryx, and Klinckowstroem206 in
1892, in Larus, mentioned an evagination in front of the epi-
physeal anlage. Hill181 in 1900 observed in a closed neural tube
two such evaginations. Whether it is justified to consider the
anlage of the epiphysis in birds as bilateral or double or whether
one of these evaginations represent the remnant of the para-
pineal organ, is a difficult question to decide. By many these
reduplications in the anlage are considered as pathological since
they occur only in isolated instances of the several species
described. The most common form in which the anlage in birds

68

FHHDKHK'K TILXKY AM) LTTHKH F. WAIJKKX

presents itself is a single evagination in front of the posterior
commissure. The further differentiation of the epiphysis is
given by Lieberkiihn-'- in (inline and also in much more detail by
Mihalkovic/-71 in 1X74 and 1S77. According to the description
of the latter, the principal change from the original saccular
evagination in the roof-plate consists in the conversion of the
original sac into a folliculated structure which presents many
alveoliform cell groups as a result of the rapid proliferation in
the walls of the original saccular anlage. Henrichs ('96) '"
found that the follicles first developed as hollow buds in com-
munication with the main cavity of the original epiphyseal
anlage. Later these buds become branched and in this way a
rich follicular system is developed.

-Cor

Fitf. 3"> The epiphyseal complex in an oinliryo of Sterna hirundo. according to
Klinrkowst n>riii. l.v.M .

According to Henrichs, the paraphysis first appears as a solid
sprout and later acquires a lumen. Cameron"1 showed in the
chick that the epiphyseal anlage is a double outgrowth, the left
being the larger. These two evaginations ultimately coalesce.
Practically the same condition is observed in amphibia. ( lar-
jano"1 makes the observation which in the main covers the con-
ditions observed in birds, namely, that as compared with the
lower vertebrates the pineal body is a profoundly altered organ
in bird- and mammals.

One M|' the authors in a recent work on the diencephalon re-
produces illustrations of reconstruction models which show the
development in the pineal region of <!<il!n* (jtillns. The first

... THE PINEAL BODY

69

evidence of <the epiphyseal complex in the chick makes its appear-
ance at five days and twenty hours as a sprout from the caudal
extremity of the interbrain roof-plate. This sprout contains a
narrow canal and at this very early period shows an apparent
differentiation into an expanded distal portion, a stalk, and an
expanded proximal portion.

Fig. 36 Mesial view of forebrain reconstruction of chick of 5 days and 20
hours. X 100. The unshaded area shows the cut surfaces of the reconstruction,
according to Tilney, 1915.

2, chiasmatic process; 4, chiasm; 7, epiphysis; 13, infundibular process; 20,
lamina terminalis; 25, mammillary region; 32, post-chiasmatic eminence; 33, post-
chiasmatic recess; 36, post-infundibular eminence; 38, pre-optic recess; 39, para-
physis; 41, supra-optic crest; 42, supra-optic recess; 44, telencephalon ; 45, tuber-
culum postero-superius ; 46, tubercle of the floor of Schulte.

iO FREDERICK TILXEY AND LUTHER F. WARREN

At this time the pineal region presents a well-marked para-
physis, a velum transversum, and a dorsal sac. At the stage of
eight days in the chick a marked change is noticed, for at this
period of development the pineal anlage has the appearance of a
wide and expansive evagination in free communication with the
third ventricle.

39

Fig 37 Mesial view of forchrain reconstruction of chick of 8 days. X 50.
The unshaded area shows the cut surfaces of the reconstruction, according to
Tilney. Ull.V

2, chiasmatic process; 3, cerebellum; 4, chiasin; 7, epiphysis; <), foramen of
Moiiro; 11, infundibular stem ; 12, infundibular canal; 13, infundibular process;
24, midbrain; 2"), mammillary region; 20, mammillary recess; 32, post-chiasmatic
eminence; 35, post-infundibular recess; 36, post-infundibular eminence; 38, pre-
chiasmatic recess; :>!>. paraphysis: 41, supra-optic crest; 42, supra-optic recess;
1 1, telencephalon.

The brain of the chick at fourteen days and eighteen hours
shows a marked alteration in the pineal region, as a result of
which the development of the epiphysis seems to overshadow all
other structures in this region. The walls of the evagination
which characterize the pineal organ in the eight-day chick have
become greatly thickened near the distal extremity of the epi-
physis so that no\v this portion of the organ is practically solid

THE PINEAL BODY

71

with the exception of a very small lumen which extends almost
throughout its entire extent. A very large pineal recess is
present. The dorsal sac and paraphysis are both much reduced
in size. There is no evidence of any distal portion of the pineal
organ at this period. No sign of an evagination or anlage which
might be interpreted as the parapineal organ was found in this
study.

39

ana.

4238

41

-44

Fig. 38 Mesial view of forebrain reconstruction of 14 days and 18 hours chick.
X 25, according to Tilney, 1915.

1, aqueduct of Sylvius; 2, chiasmatic process; 3, cerebellum; 4, optic chiasm; 7,
epiphysis; 9, foramen of Monro; 12, infundibular canal; 14, infundibular process,
saccular surface; 15, infundibular process, pituitary surface; 24, midbrain; 26,
mammillary recess; 27. mammillary body; 32, post-chiasmatic eminence; 33, post-
chiasmatic recess; 36, post-infundibular eminence; 38, pre-chiasmatic recess; 39,
paraphysis; 41, supra-optic crest; 42, supra-optic recess; 44, telencephalon.

72 FREDERICK TILNKV AM) Ll'THKR K. WAKKKX

8. Tin ilcn-lojHin nl »f tin r /ii/>/i ijKcal complex in nnunmals

The only portion of the epiphyseal complex \vliich appears in
the anln^c in mammals is, in all probability, the proximal part
of the pineal organ, for there is no evidence of the anterior or
parapineal clement. Mihalkovicz-7' in 1877 .nave a description
of the development of the organ in mammals and called attention
to the fact that it resembled very closely that of birds. At first
the anlage is a simple evaluation, then several lateral diverticula
about the same size make their appearance and later give rise to
many follicles. The lumen of each follicle from the beginning is
smaller than that in birds and ultimately is obliterated so that
there are finally solid follicles surrounded by connective tissue
and blood vessels. The epiphysis always retains its connection
with the interbrain by means of a set of peduncles. These
peduncles vary in their arrangement and number according to
the form of the animal. In man they are described by Test ut393
as being three pairs, known respectively as the superior, middle,
and inferior peduncles of the pineal body. Alihalkovicz gave
his description of the relations of the anlage to the roof-plate as
Jie observed them particularly in the rabbit.

Kraushaar-21 in 1885 confirmed these findings in the mouse
and Kolliker-11 in 1879 in the rabbit and sheep. d'Krchia109 in
ls|)0 found that the epiphysis in the guinea-pig is laid down as
a solid bud or sprout, while in man it has in its anlage a small
lumen from the beginning (fig. 39).

Neumej'cr'-"^' in 1S99 found in the rabbit that the epiphyseal
anlage was a long, tubular structure with a narrow lumen and
considerably convoluted. The original lumen of the anlage is
ultimately reduced until it occupies the proximal portion only
where it is known as the ivcessus pinealis, according to Heichert,326
or the recessus infrapiiiealis, according to Mihalkovicz.275 This
distinction takes account of the description already given by
lleidierl of the sii| >ra pineal recess.

In >tudying the development of the diencephalon in the
domestic cat one of the authors illustrates by reconstruction
models of the following embryos: In rcli* <l'>niexiicti, the pineal

THE PINEAL BODY

73

organ shows the first appearance of the epiphyseal complex at
the stage of 30 nun. embryo where it takes the form of a wide,
single Pagination immediately cephalad to the posterior com-
missure. This evagination contains a recess in free communica-
tion with the third ventricle (fig. 40).

In a cat embryo of 51 mm. a notable change has taken place
in the epiphyseal anlage shown in the fact that the original
single evagination has now become subdivided into two smaller
sacs separated by a marked thickening in the original diver-
ticulum. This is shown in figure 41.

Fig. 39 The pineal body in Cavia cobaya, according to d'Erchia, 1896.
Ds , dorsal sac; Ch., commissura habenularis; Sch., pars intercalaris; Ep.,
epiphysis cerebri; M, midbrain.

In so far as is known no similar occurrence has been noted in
mammals with the exception of a single report by Cutore74 in
the new-born Bos iaurus in which two distinct evaginations in
the epiphyseal complex were observed. This appearance was
interpreted by Cutore as indicative of an anlage both for the
pineal and parapineal organs, and if such an interpretation
seems acceptable, it might be applied to the appearances just
mentioned in the embryos of the domestic cat. The tendency
for this double diverticulum to persist through the development

74

FREDERICK TILNEY AND LUTHER F. WARREN

of the later st :!<:<•> in the cat is shown in figure 42, illustrating the
conditions in a 70 nun. embryo. Models by one of the authors
show the existence' of this twofold structure in the cat as late as
120 nun. embryo.

7

25

35

Kig. 40 Mesial view of forchrain reconstruction of 30 nun. cat embryo. X 50.
The unshaded area shows the cut surfaces of the reconstruction, according to
Tilney, 1915

2, chiasmat ic process; I, chiasm; 5, corpus interpedunculare; 7, epiphysis; 9,
foramen of Moiiro; 1 1 . infundibular stem ; 12, infundibular canal ; lo, infundibular
process; '_'(), lamina terminalis; 25, mammillary region; 32, post-chiasmat ic emi-
nence; 33, post-chiasmatic recess; 34, post-infundibular eminence; 35, post-in-
fumlibular recess; 39, dorsal sac ; 40. recess of t he infundibular process; 41 supra-
optic crest ; }2. supra-optic recess.

The most recent study of the pineal region in mammals is that
of John Warren,117 in which he brings to a conclusion his excel-
lent series of papers upon the interpretation of this region of
the brain in vertebrates. Of the human embryo he gives the
following description (fig. 43):

THE PINEAL BODY

75

The primary arches can be demonstrated in early human embryos
from 10 to 15 mm. in length.

Of the embryos of 15 mm. and over examined there were about thirty
in which the brain was in suitable condition to warrant making obser-
vations, and in addition to these a number of others were studied but
excluded on account of injury or distortion of the forebrain. In the
thirty specimens only eight showed any possible signs of a paraphysis
and most of these were mostly rudimentary in character. By counting
every possible case we get a result of 27 per cent. The fact remains,

''Ifjf^.

*%i<&«;-;.

'«»,:

n&&$$m&K,

•-ittin

- . ••.'. • •:vMfc;A--.\1:-: !rt^

42

£7

-20

Fig. 41 Mesial view of forebrain reconstruction of 51 mm. cat embryo X 50.
The unshaded area shows the cut surfaces of the reconstruction, according to
Tilney, 1915.

2, chiasmatic process; 4, chiasm; 5, corpus interpedunculare; 7, epiphysis; 9,
foramen of Monro; 11, infundibular stem; 13, infundibular process; 20, lamina
terminalis; 27, mammillary body; 32, post-chiasmatic eminence; 33, post-chias-
matic recess; 35, post-infundibular recess; 36, post-infundibular evagination; 39,
dorsal sac; 40, recess of the infundibular process; 42, supra-optic recess

76

TiLXKY AM) U'THKK F. YVAKKKX

however, thai the structure can be found in human embryos, though
in a rudimentary and inconstant condition.

'I'he so-called post velar lultules or divert icula can lie clearly fol-
lowed in every decree of complexity in embryos of 1!) nun. up to 44
nun. and appeal' in every specimen studied in those statics. They

40 33 32

i !_' Mesial view of forebraiii reconstruction of 70 mm. cut cmliryo. X 2.">.
Tlie unshaded ;irc;i shows the cut surface of the reconstruction. According to
Tilney. I'.ll.V

_'. cliiasmat ic process; (. chiasm ; .">. corpus interpedunculare ; 7. epiphysis; !»,
fora ii ii MI of Moiiro : l.'i. infinidiliular process; '_' 1. midl>niin : L'7, iiiiiiiiiuillary liody;

:!'_'. post-chiasmatic eininence: :;:;. post-chiasmatic recess; 34, post -infundibular

eminence; •'!"'. po>l-infuinlil)iilar recess: :;.s, pre-chiasmatic recess: 10. recess of
infundibular process; 41. supra-optic crest; !_'. supra-optic recess.

Iteii'in at the dieiicephalic lip of the \-eliim, have definite limits ;md
involve ;i relutively short extent of the oi-;d end of the dieiicephalic
roof-|)lale. They always appear as out u'rowt hs from the lirain roof
and are to lie distinguished from ingrowths due to plexus formation.

Vs'isi-rcn's117 deseriplioii of the coiidit ions in ihc sheep is as
follows:

THE PINEAL BODY

77

The primary arches consist of the paraphyseal arch, the postvelar
arch, the epiphyseal arch and the pars intercalaris (synencephalic arch)
and together with the velum are formed in the roof of the forebrain of
early sheep embryos.

The paraphysis can be followed in practically all sheep embryos
from 20 mm. up to 48 mm. It is characterized by its short, broad, and
irregular outline and its solid structure, the cavity being in most cases
reduced to a minimum.

E.

Fig. 43 Reconstruction showing development of the pineal region in man. 23
mm. embryo, according to John Warren, 1917.

L.T., lamina terminalis; P., paraphysis; V., velum; P.V.A., Post-velar arch;
E., epiphysis; P.C., posterior commissure.

78 FREDERICK T1LNEY AND LUTHER F. WARREN

The diencephalic choroid plexus and lateral belencephalic plexuses
are well marked and develop essentially as described in other verte-
brates. There is no trace of the median teleucephalic plexus so notice-
able in Amphibia.

The epiphysis forms a short hollow stalk with thick walls and in-
clined slightly backward over the posterior commissure.

The superior and posterior commissures are formed as in other
vertebrates. The posterior commissure is characlerixed by its pre-
cocious development and by the extent that it invades the pars inter-
talaris of the forebrain in early embryos (fig. 44).

It will be observed that in the ontogenesis of each element in
the epiphyseal complex, three distinct parts may be discerned in
each of the two organs entering into it. Thus, the pineal organ
may have an end-sac, a stalk, and a proximal portion, and the
same is true of the parapineal organ. Considered in the light
of comparative embryology, it will be seen that the most con-
stant part throughout the phylum is the proximal portion of
the pineal organ. This, beginning with a moderate prominence,
as in the cyclostomes, rises to a very prominent element in sela-
chians and maintains this prominence with somewhat of an
increase in its importance throughout the entire series, with the
single exception of crocodilia, in which the pineal body is said
by Sorenseiv"'3 to be entirely wanting. On the other hand, the
proximal portion of the parapineal organ shows a strikingly low
percentage of occurrence throughout the phylum. It may
perhaps be accredited to the cyclostomes, if one takes into
account the thickened portion of the unusually large commissura
habenularis, but thereafter in the series it seems to disappear
entirely.

The next most constant structure in the epiphyseal complex
is the end-vesicle of the pineal organ. This maintains a high
degree of prominence in cyclostomes, selachians, ganoids, teleosls,
urodeles and anura. It shows a conspicuous tendency to atten-
uate in the prosaurians and saurians and finally in the ophidians,
and in all the orders thereafter it is notable for its absence. The
analogue of the pineal end-vesicle, namely, the parapineal end-
vesicle, is much more irregular in its occurrence throughout the
phylum, but on the other hand, in certain forms it presents such

THE PINEAL BODY

79

striking characteristics as to make it one of the most prominent
and important elements in the epiphyseal complex. Its appear-
ance in cyclostomes is almost as striking as the pineal end- vesicle,
but its tendency to irregularity is noted by a complete absence

V.

P.

o.c.

s

Fig. i4 Reconstruction showing the development of the pineal region of a
sheep embryo of 48.4 mm., according to John Warren, 1917.

P.M., foramen of Monro; P., paraphysis; V., velum; S.C.,commissura haben-
ularis; E., epiphysis; P.C., posterior commissure.

80 FREDERICK T1LXEY AND LUTHER F. WARRKN

in the selachians. It makes a somewhat abortive appearance in
the ganoids and teleosts. In urodeles and annra it disappears
altogether but when again it does occur as a feature of the
epiphyseal complex, it has assumed such proportions as to
make it by far the most prominent structure in this area of the
brain. In the prosaurians and the saurians, it is a most con-
spicuous element. As may easily be presumed, the pineal stalk
and its analogue1, the parapineal stalk, follow very closely the
frequency of occurrence of the two end-vesicles. Thus the
pineal stalk is present in cyclostomes, selachians, ganoids,
teleosts, urodeles, anura, prosaurians and saurians, but disap-
pears in the higher forms. The parapineal stalk is present in
the cyclostomes, but does not appear in selachians. It has an
abortive form in ganoids and teleosts, is absent in urodeles and
anura, occurs in its most marked representation in prosaurians
and saurians, and thereafter disappears altogether.

6. THE COMPARATIVE ANATOMY AND HISTOLOGY OF THE

EPIPHYSEAL COMPLEX

In the light of the embryological development of the epiphy-
seal complex, the difficulties in the adult morphology of these
organs are much diminished. The following description will
deal with the comparative anatomy and histology of the two
epiphyseal elements in the different classes of vertebrates and
will be based upon the observations of the different species
already investigated.

1. The comparative anatomy and histology of the epiphyseal

complex in cyclostomes

The pineal organ in cyclostomes presents the three charac-
teristic parts, namely, a proximal portion, a stalk, and an end-
vesicle. Each of these is more or less highly specialized. The
end-vesicle has t lie form of a, small ellipt ical vesicle. In its longest
diameter cephalocaiidad, it is ().:>."> nun. in length. This measure-
ment was made in /'<//•<>/>/ //z<»t by Studnicka.:ivl It presents

THE PINEAL BODY

81

certain parts, as for example, a dorsal wall and a ventral wall,
which are to be distinguished from each other by certain histo-
logical features. These two walls bound a cavity or lumen
concerning which there has been much discussion and to which
the name of atrium is usually applied. Ahlborn2 in 1883 states
that this atrium presents a peculiar lacunar appearance.

Fig. 45 Cross section of the epiphyseal complex in Petromyzon, according to
Ahlborn, 1883.

Po., pineal organ; Ds., dorsal sac; Pp., parapineal organ; Ha., habenular
ganglion.

Beard18 in 1889 thought the atrium contained a coagulated
fluid, and Owsiannikow295 in 1888 was of the same opinion.
Gaskell,145 however, in 1890 found that the atrium of the pineal
organ in Ammocoetes was in reality filled with cellular tissue
and, according to this observer, the pineal organ in these forms
had a general structure which was similar to the composite
eye of Arthropods. Leydig239 in 1896 found the atrium filled
with what he calls secretory fibers extending inward from the
retinal cells of the organ. Studnicka384 in the later stages of
Ammocoetes found in the lumen of the end-vesicle a peculiar,

MEMOIR NO. 9

82

FREDERICK TILNEY AND LUTHER F. WARREN

fibroid, hyaline substance attached to the free end of the cells in
the retina. This took on the form of a coagulum in the semifluid
contents of the atrium. Later Studnicka888 in 1899 described in
Petronn/zon nuirinnx similar hyaline bodies and showed that they
were the thickened extremities of the retinal cells projecting into
the lumen of the end- vesicle.

Fijr. 10 Sagittal section of the epiphyseal complex of IVtromy/on flaviatilis

.showing syiicyt ial masses in 1 lie At num. according t o St udiiicka, IS'.!!).

fill., pollucida; ]'<>.. ])iueal orjian; //</.. retina; /'/'•• parapineal organ.

In this way these processes from the retinal cells formed a
virtual syncytium which almost completely fills the atrium. Of
the two walls forming the end-vesicle, the ventral wall presents
certain characteristics which seem to justify the recognition in
it of a retinal structure. Tor this reason the ventral wall is
known as the rrl./tui of the pineal origin in cyclost nines. The
dorsal wall has an entirely different structural character, and
because it is (jiiite without pigmental ion is known as the />< Ih/c/i/n.

THE PINEAL BODY 83

The retina of the pineal organ in cyclostomes shows its most
marked development in embryonic and larval stages. Beard17
in 1887 found in Ammocoetes rod cells, and Owsiannikow295 in
1888 showed in Petromyzon fluviatilis that there were five dis-
tinct layers of cells and fibers in the retina. The first of these
layers consisted of nerve fibers; the second, of large nerve cells;
the third was fibrous; the fourth consisted of small cells inter-
spersed among the large rod-shaped cells, and the fifth was an
ependymal layer. Gaskell145 in 1890 was able to find rod cells
only in the retina of Ammocoates, and he was of the opinion
that the so-called pineal eye in this form was a compound struc-
ture in which the light-receiving bodies were formations com-
parable to the rhabdites of the Arthropod eye. Studnicka
('93)384 recognized four layers of cells and fibers in the retina of
cyclostomes. The first of these was a layer of nerve fibers, the
second were basal cells, the third small cells, and the fourth,
large cylindrical cells. Leydig239 in 1896 found two types of
cells, an inner cylindrical and an outer layer of round cells.
Retzius,331B however, in 1895, could find no evidence of the sensory
organ in the so-called pineal eye of cyclostomes and he did not
consider it to be an eye. Mayer264 in 1897 found ganglionic
cells in the retina, and Studnicka388 in 1899 found still more
evidence of the retinal nature of the ventral wall of the end-
vesicle.

The pellucida becomes best developed in Petromyzon marinus,
for the dorsal wall of the pineal organ appears in the more or less
constant form of a plane or convexed lens, the flattened surface
of which is ectally directed. In Petromyzon planeri and fluvia-
tilis, the pellucida is extremely irregular in its thickness as well
as in its form. It must not, therefore, be maintained that even
in those forms where the pellucida has a lenticular shape and
arrangement that it is actually a lens structure. One feature
about it, however, suggests that it is an organ designed for the
transmission of light rays, namely, its almost complete lack of
pigment except perhaps at the peripheral edges where it passes
over into the ventral wall or so-called retina of the pineal eye.
This lack of pigment led Carriere57 in 1890 to call the dorsal wall

S4

FREDERICK TILXEY AND LUTHER F. WAKRKX

of the pineal organ the ptUnmln. Histologically the pellucida
is, according to Ahlborn- made up of cells of considerable size
together with connective tissue. Owsiannikow- '" found both
libers and small cells. Whit well4-1 and Beard1 s in 1888 found

f-T /--r'. '•••'••'« (•->'"'

" '

.<J»\i1

I1 ij:. 1 7 IJi-l in:i :ind pclluciiln of the pinciil orjiau in :i l'ull-m-n\\ n I'ct roiny/mi
iii.-iriiius, :icc(,riliiiu to St udnicka, 1899.
/'• //., |n-lliicitl:i : l\i t., retina.

thai the pellucida consisted of cylindrical cells. ( iaskell11'"1 in
ls(. )() observed cylindrical and small cells, and St udnicka388 as
well as Rct/ius:;i" found tli.-it (lie structure was made up almost
exclusively of l.-irge cylindrical cells.

THE PINEAL BODY 85

The white pigment of the retina. Mayer265 in 1864 observed
that the epiphyseal complex in Petromyzon contained many
calcium bodies. Subsequently Ahlborn2 made the observation
that there were a large number of small bodies of a peculiar
white substance which he called the white pigment and regarded
it as similar to the brain sand of the higher vertebrates. This
white substance filled in the cells of the retina in such a way as
to prevent the passage of transmitted light and to give the
appearance of a glistening white when illuminated. Accord-
ing to Studnicka,388 this pigment does not appear in Ammoccetes
younger than those of 50 mm. in length, but thereafter gradually
increases in amount until the adult form is attained. Leydig239
in 1896 differentiated two kinds of pigment bodies — those which
are small in amount, of a dark brown black color and those of
the second type which by transmitted light appear to be a
brownish yellow. By direct light these pigments appear to be
white.

The stalk of the pineal organ in cyclostomes. In cyclostomes
the pineal stalk becomes much reduced in size and it completely
loses its lumen in the adult. It becomes conspicuous, however,
by the development in it of certain nerve fibers whose collected
bundle was first called by Leydig239 in 1896 the 'Zirbelnerv.'
This structure, later in 1898, was called by Gaupp147 the tractus
pinealis and finally the nervus pinealis by Studnicka.388 This
pineal nerve established a fiber connection between the peculiar
organ situated beneath the roof-plate and known as the pineal
eye in cyclostomes, and the roof of the brain. The fibrous
nature of its structure was first observed by Whitwell421 in 1888.
Owsiannikow295 noted that in addition to the nerve fibers there
were to be observed in the pineal stalk a bundle of fine nerve
fibers. The diameter of these fibers, according to his measure-
ment, was 50 micra. Running with the nerves were numerous
blood vessels. Gaskell145 could not distinguish whether nerve
fibers or processes of cells made their course within the nerve
sheaths. It was only at the entrance of the nerve into the eye
that he found a lumen. Studnicka,388 however, maintained that
the stalk was an actual nerve and therefore applied to it the term

86 FREDERICK TILXEY AND LUTHER F. WARREN

He was able to trace the nerve fibers from the
so-called retina of the pineal eye into the stalk. Retzius33111 in
1895, using (lolgi preparations in Ammoccetes, was able to
demonstrate the actual presence of nerve fibers of the pineal
nerve which he followed from the pineal organ to the brain.
This observation in similar preparations was confirmed by
Mayer-'14 in 1897. Ley dig239 in 1896 found in Petromijzon
fluviatilis that nerve fibers were present only in the proximal
third of the stalk, while Johnston195 in 1902 in Lampetra wilderi
found that the nerve fibers in the proximal portion of the stalk
seemed to be obliterated in some preparations. The pineal
nerve has a definite sheath of its own consisting of elements simi-
lar to those covering the brain. There is a membrana limitans
extcrna composed of neuroglia. Surrounding this is a layer of
pia mater and still more externally a process from the dura
mater.

The central endings of the nervus pinealis have been traced
by Ahlborn2 and Gaskell145 to the posterior commissure. Gaskell
showed that the nerve was connected with the right habenular
ganglion and that this nerve structure was, therefore, the optic
ganglion of the pineal eye. Studnicka388 followed some of the
fibers to the inner portion of the posterior commissure. He
thought that the pineal nerve ended in the left habenular ganglion
while the nerve of the parapineal organ ended in the right struc-
ture of this name. Mayer264 traced the fibers by means of silver
impregnation to the posterior commissure. The proximal
portion of the pineal organ in cyclostom.es is much reduced in
size because of the close approximation between the posterior
commissure and the commissura habenularis. A small recess,
however, marks the position of the proximal portion in these
forms and is situated between the two commissures just men-
tioned. This is the recessus pinealis. The pineal organ in
cyclostomes has been called the epiphysis, the epiphysis cerebri,
and the superior vesicle of the epiphysis, according to Ahlborn
in 18S:-5.'

The parapincdl organ, in cyclostomes. The more cephalic of
the two epiphysea1 elements in cyclostomes has been called by

THE PINEAL BODY

87

Studnicka388 the parapineal organ. According to Ahlborn,2 it
was the inferior vesicle of the epiphysis. Owsiannikow295 termed
it the visceral vesicle, while it was called by Kupffer222 the para-
physis. It presents an end-vesicle, a stalk, and a proximal
portion. It its general form it resembles the pineal organ and is
situated as a more or less distinct vesicle between the pineal
organ and the roof of the brain in the region immediately cephalad
to the habenular ganglion and the commissura habenularis.
The vesicular portion is in relation with the habenular ganglion,
being situated dorsal to it, while the stalk and proximal portion
are in relation with the commissura habenularis. In size the
parapineal organ is considerably smaller than the pineal organ,
and though it varies considerably in this respect, the following
tabulation made by Studnicka388 shows the general dimensions
of the organ in Ammoccetes and Petromyzon planeri. These
figures apply to the end-vesicles.

PINEAL ORGAN

PARAPINEAL ORGAf/

23 mm Ammocoetes

mm.
0 23

mm.

0 105

26 mm Amrnocoetes

0 15

0 12

30 mm Ammocoetes . . .

0 15

0 09

49 mm. Ammocoetes

0.22

0 15

94 mm. Ammocoetes

0.24

0 14

117 mm. Ammocoetes .

0.31

0 20

Petromyzon planeri

0.35

0.25

Ahlborn2 in 1883 found that the parapineal organ in general
has the same form, although it is smaller than the pineal organ
while the cellular elements in the two structures correspond very
closely. The lumen of the parapineal organ contains a fibrous
tissue having many histological features in common with that in
the pineal organ. Beard18 in 1889 found the parapineal organ
in Ammoccetes only a little less developed than the pineal
organ, in which opinion Gaskell145 concurs. In Petromyzon
fluviatilis, Owsiannikow295 in 1888 found that the parapineal
organ was smaller than the pineal organ, but in no other way
different from the latter. The end-vesicle contained a retina

; i;i;i>i.i;icK TILNKV \xi> LTTHKR F. WAKKKX

in which there were several layers of cells, including rod- and
cylindrical-shaped cells measuring from 7.4 to 8.3 micra in
diameter. There" were also some larger cells scattered among
the rod cells with a mean diameter of 14 micra. He found in
the ret ina many nerve fibers which made their way into a definite
fasciculus constituting a parapineal nerve. Studnicka388 did
not agree wholly with Owsiannikow in the idea that the para-
pineal end-vesicle was as well developed as the corresponding
structure of the pineal organ. He states that the difference
between these two structures is the fact that the parapineal

Pe<l

Ha

Pp Pf

Fig. 4$ Sagittal section of the pineal and parapineul organs in Aminoccctes
with silver impregnation, according to lU't/ius, 1895.

Ls., lamina terminalis; I'f., paraphysis; /'/*., parapineal organ; Ifn., habenular
ganglion; l\'</., ret inn; /'///., pellucida; \./>/n., pineal nerve.

end-vesicle is not as highly developed a retinal structure as is
the case with the pineal end-vesicle. Studnicka, however, finds
that there is in the dorsal wall of the parapineal vesicle a definite
pellucida made up of several layers of cells. Those cells iden-
tified in the retinal layer by Owsiannikow295 and Studnicka388
aa the rod cells were recognized by Retzius™1" in 1895 by means
of the ( lolgi method as bipolar cells.

By this method l!et/iiis:':il" was able to trace nerve fibers which
took origin in the left li;ibenul;ir ganglion and passed to the
p.'ir.-ipiiieal end- vesicle. Leydig-"1'-' in l'<'lr>itni/.:-<m. fluviatilis
found that the parapinea.1 end-vesicle was less de\-eloj)e(l, but at

THE PINEAL BODY 89

its base he was able to discern fibers which seemed to cross to
the opposite side. These nerve fibers extended backward from
the cells in the parapineal organ. Ley dig was unable to identify
any structure which he considered a retina or a lens. The stalk
in the adult form becomes reduced to a mere strand containing
fibers which by many authors are considered to be nerve fibers.
The primitive lumen present in the stalk of the parapineal
organ very early disappears and the proximal portion rapidly
becomes inconspicuous and finally is lost by the marked develop-
ment of the commissura habenularis.

The majority o;f investigators who have studied this part of
the brain in cyclostomes are in accord along several general
lines. They believe that the cells found in the parapineal
end-vesicle are ependymal cells, spindle or rod cells, and some
sensory cells. It is also their opinion that there are nerve fibers
connecting these cells situated among which are larger ganglionic
elements from which the fibers may take their origin. In a
general way the same constituents occur in the retina of the
parapineal organ as are present in the pineal organ. The main
differences between these two structures consist in the size and
disposition of their respective elements. In the adult the para-
pineal organ is situated upon the most anterior portion of the
membranous forebrain roof while directly in front of it is the
paraphysis and above it the pineal vesicle. Situated in this
position the two end-vesicles of the epiphyseal complex have
the appearance of a pair of eyes which are rudimentary and
which, in attempting to assume visual function, have morpho-
logically fallen short in the attainment of that object. It should
be noted that their position places them in the midsagittal
plane, one behind the other, and that according to the most
reliable evidence concerning cyclostomes available at the present
time, there is no definite tendency toward lateralization in one
or the other of these elements in the epiphyseal complex. The
two end-vesicles, practically in contact with each other, occupy
a deep fossa formed by a depression on the inner surface of the
skull. This fossa is especially welt marked in adults and more
particularly in Petromyzon marinus.

(.H) FREDERICK TILNEY AND LUTHER F. WARREN

What has been termed a parietal cornea of the pineal eye con-
sists of a layer of almost fiberless tissue of considerable thickness
between the dorsal surface of the pial capsule and the inner
surface of the bony depression in the skull. The epidermis
immediately above this so-called cornea is quite without pig-
ment, forming a small, circular area in the frontal region of the
head situated almost immediately in the midsagittal line. This
area was recognized long before its significance was understood
and was described by Whit well421 in 1888, by Ahlborn2 in 1883,
and by Gage135 in 1893. Gaskell145 in 1890 erroneously likened a
cranial thickening above the pineal organ in Ammoccetes to the
cuticular lens of Arthropods. Studnicka884 in 1893 found that
the cornea is discernible in the 25 mm. Ammocoetes. Gaskell,145
in his discussion of the origin of vertebrates from a crustacean-
like ancestor, makes the statement that in Ammoccetes there
are two pineal eyes, one, dorsally placed, much larger and in-
tensely white in color, lies in front of the right habenular ganglion.
The other, ventrally placed, is an insignificant structure. The
first is similar to the crustacean parietal eye in its pigmentary
character. The second is similar to this eye in Crustacea because
of the termination of the nerve endings with the attached rhab-
dites. According to Gaskell, the type of eye is clearly arthro-
podic. The arrangement of the nerve endings, the shape of the
internal cavity, and the position and simplicity of the attached
rhabdites all point to larval characteristics and, therefore, to an
ancient type. The anterior wall is not a lens. Gaskell believes
the lens is cuticular in character and, if so, this is all the more
reason for believing that the pineal eye is definitely arthropod in
type.

A Inch emphasis has been laid upon the occurrence in cyclo-
stomes of these two structures which have so many characterist ics
suggestive of visual function. The statement has been made
that this is competent evidence upon which to establish the
claim that in vertebrates the parietal or third eye was primi-
tively paired. It is to be noted, however, that in no other class
of vertebrates does the duality of the parietal visual apparatus,
if such indeed it may be considered, attain such a high degree of

THE PINEAL BODY 91

development. One or the other element of the epiphyseal com-
plex may show the tendency toward the development of visual
characteristics, but in no other form do both of these elements
take on these features so suggestive of visual function.

Differences observed in the epiphyseal complex of the various
species of cyclostomes already investigated. Although all of the three
European forms of Petromyzon have been carefully studied by
several investigators, the differences between them are not
striking. This statement also applies to the North American
form, Lampetra wilderi, described by Johnston195 in 1902.

1. Petromyzon planeri. Ahlborn ('83), 2 Beard ('89), 18 Whit-
well, ('88)421 and Studnicka ('93). 384 The epiphyseal complex as
a whole is not separated as far from the brain as in other forms,
due to the fact that the paraphysis and dorsal sac are but little
developed. The parietal fossa is very shallow and is absent in
Ammoccetes as is also the white pigment.

2. Petromyzon fluviatilis. Ostroumoff ('87),291 Owsiannikow,
('88),295 Leydig, ('96)239 and Studnicka ('99).388 In this form the
evagination of the roof is very high and the fossa in the skull of
considerable depth. The atrium contains a definite syncytium
made up of processes not only from the retinal cells, but also
from those situated in the pellucida as well.

3. Petromyzon marinus. Studnicka ('99). 388 Although the
dorsal sac is extremely high, the depression in the skull is no
deeper than in the case of Petromyzon fluviatilis.

4. Petromyzon wilderi. Johnston ('02). 195 In this form the
stalk of the pineal organ has not the significance as in other
forms, for the pineal nerve is absent and the stalk contains no
nerve fibers.

5. Mordacia mordax. Spencer ('90). 369 In this form the
pineal organ presents a thin, pigmented upper wall correspond-
ing to the pellucida of Petromyzon, and a thicker ventral wall in
the form of a retina. No definite statement is made as to the
presence of an atrium, although the lumen of the organ is said
to be filled by a coagulum. There is no evidence of any para-
pineal organ, but on the surface of the head, midway between
the paired eyes, there is a parietal spot.

92 FREDERICK TILXKV AXD LUTHER F. WARREX

6. Mi/.rinc ghtiinosa (Bdellostoma) . Kupffer C04).2-1'1 In this
form there is no anlage of the epiphysel complex whatsoever.
The roof is entirely Hat. hut in spite of the absence of the cpi-
physeal complex, both habenular ganglia are present. Such
descriptions of the epiphysis in Mi/xine as appear in the litera-
ture seem to be an error. Andrae Retzius33lA in 1822 described
the pineal body in connection with the habenular ganglion,
interpreting the hitter t:> be the epiphysis. Leydig23y in 1890
believed that he had found in Myxinc the i)ineal body, but in
reality mistook a large lymph space near the surface of the
head for this organ. Studnicka,388 however, in his studies was
unable to rind any evidence of the pineal body in M^i/.r/ne.

2. The comparative histology and (UKitn/ny of the epiphyseal

complex in

Since the pineal organ is the only part of the epiphyseal com-
plex to make its appearance in selachians, the structure is much
more simple than in cyclostomes. Furthermore, such parts of
the pineal organ as do develop in selachians are relatively rudi-
mentary. All of the three usual elements of the pineal organ,
however, may be identified; that is to say, a hollow end-vesicle,
a stalk, and a proximal portion. The end-vesicle in no instance
presents the two distinct walls, namely, the ventral and dorsal
walls distinguishable in cyclostomes, and the end-sac itself is
much smaller than in the forms already considered. Slight
differences in the thickness of the wall of the end-vesicle may be
observed in different places, but with no great uniformity. In
consequence of this lack of differentiation, there is no evidence
of the formation of a retina, of a pellucida, or of a white sub-
stance, nor do any nerve fibers make their appearance in con-
nection with the end-vesicle. In fact, it is a question whether
the pineal organ of selachians is a primitive structure or one
that is distinctly retrograde. In form there may be a consider-
able difference in the terminal vesicle; it may be wedge-shaped,
cylindrical, conical, or flattened, but in all instances it is hollow,
eiintainiiig a lumen, in spite of the statement of ('attie"" to the
contrary in his descriptions of Mnxt<'Inx, Ittt'nt, and .\cn//l//ias.

THE PINEAL BODY 93

Frequently the wall of the vesicle presents reduplication, as in
the case of Spinax niger where there is a distinct tendency to
lobulation, or as in Acanthias where the folding of the wall
results in the production of two adjacent vesicles. In a single
instance only is there a marked differentiation between the
ventral and dorsal walls. This occurs in Lamna cornubica,
particularly in the embryonic state, described by Carrington58
in 1890. In this form the under wall was thicker than the
dorsal wall. Studnicka389 found some tendency to such a dif-
ferentiation in Spinax.

Histologically, the walls of the end-vesicle are made of epen-
dymal cells, but there are no cylindrical or spindle cells to be
observed in this structure. The cells described in cyclostomes
as having prolongations of such a character as to warrant the
description of ciliated cells are absent in selachians so that no
such processes make their way into the lumen of the end-vesicle,
as is the case in Petromyzon. The nuclei of these cells are
situated at varying distances from the surface of the wall so that
the ependyma gives the impression of stratified epithelium,
whereas in reality it is a single layered epithelial structure.
Some cells have a rather long process which approach, but do
not enter, the lumen of the end- vesicle. This manifestation is
taken as a probable sign of an excretory function of the cells in
question. Galeotti140 in 1896 described in Scyttium peculiar
appearances which seemed to indicate a secretory or excretory
activity on the part the cells in this portion of the pineal
organ. Among the more usual cells, according to Studnicka,389
there are many smaller cells scattered here and there of a similar
type to the sense cells in the retina of Petromyzon. The signifi-
cance of these cells is not at all clear, and Studnicka himself is
not willing to accredit them with a definitely receptor function.

The stalk of the pineal organ. Microscopically, this appears to
be a long, narrow strand connecting the end-vesicle with the
roof-plate of the interbrain. Upon microscopic examination
it is found, however, to contain a central but narrow lumen, the
entire structure, therefore, being tubular. In most instances
this stalk maintains an equal diameter throughout its entire

'.14

FREDERICK TILXEY AND LUTHER F. WARREN

extent, although in certain cases it becomes much attenuated
as it approaches the end-vesicle. A few nerve fibers course in
the dorsal wall of this hollow stalk, but these cannot properly be
considered the homologue of the pineal nerve in selachians.

The proximal /mrtion in selachians may be readily made out.
As the stalk approaches the roof of the interbrain, it gradually
becomes dilated and increased in its transverse diameter. Its
lumen becomes larger and the walls bounding it are thrown into
numerous folds. Although the transition from stalk to proximal
portion is gradual it is nevertheless distinct. In a few cases

-

• ',-,'/;/ '

/ - -^'^.f^

Fig. 49 Knd-vesicle in the pineal organ of Acanthias vulgaris, according to
Studnicka, 1893.

only, such, for example, as Centrophorns, described by Cat tie'50
in 1882, is there an absence of this reduplication of the walls of
the proximal portion. As the dorsal wall of this portion ap-
proaches the posterior commissure there appear in it a few
strands of nerve fibers constituting what may be called flic
tractiis pincalis. It is doubtful, however, whether the com-
niissura habemilaris receives any of I he libel's which enter into
tlie formation of this tract.

Tin- slinillix <>f the /i/tiKil iiri/dii ;ire the same as those in 1'elro-
nujzon., namely, a nie.mbnma liniitans exlerna., a process from

THE PINEAL BODY 95

the pia mater and another from the dura mater. Some authors,
among them Cattie,60 have described a parietal foramen. In
Acanthias vulgar is this opening in the cartilaginous skull appears
to be doubled, the two openings being separated by a small,
cartilaginous bridge. Neither Studnicka389 nor Ehlers108 was able
to discover any such openings in the forms which they investi-
gated. The parietal cornea is absent and the parietal spot is
very infrequently observed.

Differences observed in the epiphyseal complex of the various
species of selachians already investigated.

ELASMO BRANCHI

1. Scy Ilium canicula and catulus. Balfour ('78) 10 studying the
embryonic development; Owsiannikow ('88), 295 studying the con-
ditions in a 65 mm. embryo; Cattie ('82), 60 in the adult, and
Galeotti ('96),14° studying the histology. The proximal portion
in these forms is not well developed and the end-vesicle is coni-
cal. The middle piece or stalk is cylindrical in shape. The
structure, according to Galeotti, shows stellate cells and epen-
dymal cells, in addition to which, there are certain cells which
are definitely fuchsinophile, which, according to this observer,
indicate secretory function because he considers these granules
secretory in their nature.

2. Acanthias vulgaris. Ehlers108 in 1878 and Cattie 60 in 1882.
In this form the proximal portion is thicker than the stalk and
both are of unusual thickness for selachians. The end-vesicle,
according to Cattie, is solid. Its walls show much reduplication
and the lumen is solidly filled with a syncytium. There is a
definite parietal foramen.

3. Echinorhynus spinosus. Jackson and Clarke ('75) 193. The
pineal organ in this form is a long, strand-like body extending far
over the telencephalon in the midsagittal plane.

4. Galeus cam's. Cattie ('82). 60 A conical end- vesicle and a
conical proximal portion with a strand-like stalk characterize the
pineal organ in this form. The end-vesicle and the stalk are
solid while the proximal portion retains its lumen and has, in
addition, many small accessory canuliculae.

96 FREDERICK TILNEY A XI) LUTHER F. WARREN

5. Mustelus /(fv/x. ('attie ('82).f>0 In this form the pineal
organ is extremely simple, consisting of an end-vesicle, a stalk,
and a proximal portion. The end- vesicle is flat and shows no
tendency toward reduplication.

6. Ct'iilro/>//(irus granulosus. Cattle ('82). 60 The end- vesicle
in this form has a hammer-shaped appearance. The stalk is
strand-like and the proximal portion conical. The pineal organ
is hollow throughout its entire course. A marked parietal
depression lodges the structure and this is surrounded by con-
nective tissue.

7. Latnna coniubica. Carrington ('90). 58 This form pre-
sents an end-vesicle which is conical and a stalk which is cylin-
drical. Both contain an irregular lumen. The ventral wall of
the end- vesicle is thicker than the dorsal wall. The cells in this
vesicle are for the most part ependymal, although there are
many others scattered among the cells of this character. The
pineal organ is lodged in a depression surrounded by connective
tissue and there is a corresponding slight depression in the epi-
thelium above the organ.

8. Spinax niger. Studnicka ('93). 384 In embryos, larval and
adult forms, this species presents all three portions of the pineal
organ. It is slender and directed at right angles to the roof-
plate in the embryo, is slightly bent in larval forms, and is
flexed at right angles in adults. The end-vesicle is pressed into
a cartilaginous skull, although there is no actual parietal fora-
men. The parietal portion consists of ependymal cells and
neuroglia cells. A parietal spot is present in the form of an
oval white area. There is, however, no parietal cornea.

9. Xuli<l<t>iux (iriseus. Studnicka ('93). 384 The entire pineal
organ in this form is sharply flexed forward above the forebrain.
The proximal part is not particularly developed, but in other
re-|>erts has the same general form as other species.

10. I'rixliurux inddnoxtottiux. d'Krchia ('96)1()'J and Minot
('01). 277 Here the pineal organ extends directly forward in the
horizontal plane above the forebrain in the midsagittal plane.
The end-vesicle is much attenuated and the stalk is merely a
Strand-like conneetion between the former and the roof-plate

THE PINEAL BODY

97

of the interbrain. There is a small conical, proximal portion.
Cattie60 states that the parietal foramen is closed only by the
dura mater.

RAIIDAE

1. Raia clavata. Ehlers (78) ;108 Cattie ('82). 60 In this spe-
cies a thin, long stalk extends far forward and terminates in a
definite end- vesicle which is enclosed in a deep pref rental fossa.

/'/" /' lh C/i

H>u .

Fig. 50 The pineal region of Torpedo ocellata, according to d'Erchia, 1896.

Hm., hemisphere; Ff . paraphysis; V., velum transver um; Ds., dorsal sac;
Ch., commissura habenularis; 8 h , pars intercalaris posterior; Cp , posterior com-
missure; M., midbrain

2. Raia follonica. Studnicka ('95). 385 The pineal organ here
is found as a thick stalk with a lumen. There is no special
proximal portion. In the lumen there is a syncytium.

3. Myliobatis aquila. Studnicka ('95).38a In this form, as
in Raia clavata, the stalk is tubular and reaches from the inter-
brain to the roof of the skull. The end-vesicle is dorsoventrally
flattened and rests in the region of the prefrontal fossa, which
latter shows but a slight deepening in the skull.

4. Torpedo marmorata. Studnicka ('95). 385 In this form the
pineal organ fails to appear, although there are present two
well-developed ganglia habenulae.

MEMOIR NO. 9

FREDERICK TILM.V AM) LTTIIKR F. WARRKX

5. Torpc<l» <>n Ha /n. d'Krchia ('96). 109 No evidence of de-
velopmental differentiation into ;i pineal organ was found in
the early stages of this form. A well-developed paraphysis,
however, is present .

HOLOCEPHALI

1. Call&rhynchus. Parker and Haswell ('97).3°-

2. Cliiititirrti inonxlroMi. Studnicka ('96). 386 In both of these
forms there is a well-defined epiphysis and a large dorsal
sac. The pineal organ has a form similar to other :elachians;
that is to say, a fairly well-marked proximal portion, a long,
>lender stalk extending forward and expanding slightly to form
an end-vesicle at its extremity.

In all, seventeen species of selachians have been examined;
that is, ten Elasmobranchs, five Rat/*, and two Holocephali.
In two species a complete absence of the pineal organ is reported,
namely, Torpedo ocellala and Torpedo marmorata. All of the
other species present a pineal organ more or less well developed.
In one form, that is, Gale us cam's, histological evidence has been
presented showing that there is some reason to believe that a
secretory function obtains in the pineal organ of this form.
"Wherever mention is made of the paraphysis it seems to be an
organ of considerable size.

3. Comparative anntonnj and hixtolo<m of tin- epiphysecd complex

in i /< i no ids

In all the species of ( lanoids there develops a fairly well-
marked pineal organ. In one form only, namely, Amid, is there
any indication of the presence of a parapineal organ. Stannius,373
giving the first description of the structure of the parapineal
organ in Adpenser sturio in 1S.~>-1. slates that the structure is a
wide evaginat ion extending from the roof of the interbrain and
connected with the comniissura habenularis. It reach-,- for-
ward to a fossa, in the roof of the skull. Cat tie1'1" in ISS'J. also in
Aci/x nwr xhirio. and Goronowitsch188 in 1SSS, on .lr//"'//xr/-
riilln'niix, gave similar descriptions of the pineal organ. ( lar-
man113 in IX'.HI and Johnston"1 in 1(.H)I by means of the ( iolgi

THE PINEAL BODY

99

method described the structure in Acipenser rubicundus. Both
observers were able to differentiate a saccular proximal portion
resembling the recessus pinealis, a thin, dorsoventrally extend-
ing stalk, the latter producing a groove in the dorsal surface
of the dorsal sac, and finally an end- vesicle greatly dilated.
The end-vesicle was of considerable size and contained a well-
marked cavity.

Its walls showed no tendency to differentiation into a dorsal
pellucidal layer or a ventral retinal layer. According to Stud-
nicka,386 the entire end-vesicle consists of rather long cylindrical

Opt Olf

Fig. 51 The pineal region in Polyodon folium, according to Garman, 1896.
Olf., olfactory lobe; Opt., optic nerve; Htn., hemisphere; Po., pineal organ;
St., stalk.

cells with a generally oval nucleus and two processes, one a
slender extension reaching in toward the lumen of the pineal
organ and the other a more diffuse ending, extending toward
the ectal surface of the wall. Scattered here and there among
these cells, which are in the majority, are a number of large
elements more distinctly oval in character with a rounded
nucleus situated near the center. Some smaller elements are
also found scattered more numerously among both types of
cells. Studnicka describes them, first, as ependymal cells;
second, as sense cells, a larger-sized cell which he thinks may

100

FREDERICK TILXKY AXI) LTTHKU 1. WAHHKX

lie li'an^lionic cells, and, third, iieuroo-lia cells which arc smaller
;'iid »vnerally more deeply situated elements in the walls of the
end-vesicle. The stalk is si rand-like in appearance and may

a b

Fig. 52 a, Pineal organ in Acipcnscr nil>irun<lus. l>, 1'inral organ in Polyo-

d<ui foliiirn.

contain a lumen in part of its extent or else running the entire
h-nirtl, from the roof-plate end-\'(>sicle. Its walls are made up
of small neuroglia c<ills, whil(> in the mon* dorsal of the two walls

THE PINEAL BODY

101

Johnston194 found a number of nerve fibers constituting a layer
which extends from the proximal portion to the commissura
habenularis, where it apparently undergoes decussation form-
ing the so-called decussatio epiphysis. These observations were
made by means of the Golgi method. Other fibers end freely
between the cells of the stalk. These cells, Johnston thinks, are
rudimentary or degenerated nuclei, perhaps related to the pineal

:>«

R W <P

H ;.- . M fr-

-?vBrV(-::r-^ft0->^'<l ;^S ' I'"''-' •"
.--•W -'• • -MV;^ -.• --V ;-Ff4 [.-'--•

5^^

Fig. 53 Histological structure of the wall of the pineal organ in Acipensei
sturio, according to Studnicka. 1893.

eye. He found a third type of fibers in a decussation which
comes into relation with the ganglia habenulae. Herrick177 in
1891 also mentioned such fibers in Acipenser. The proximal
portion consists, in the main, of small neuroglia elements with
some nerve fibers running in it, as already described. Stud-
nicka386 does not think that there is any indication of a glandular
activity in this part of the pineal organ which is in any way
comparable to that of the proximal portion in the pineal organ
of selachians.

102 FREDERICK TILXEY AND LUTHER F. WARREN

Differences observed in the cj>i]>hyseal complex in tJic
sj)«-i< * <>f </<i//o/</s nl /•(in/// investigated

1. Adpenser xtttrio. /v////r////.s-. and rul>icundux. Cattle ('82), 60
(ioronowitsch ('88);153 Garman ('96), »« and Johnston ('01). ^
The conditions in those forms have been described above.

2. Lepidoxtcux osseus. Balfour and Parker ('82). 12 Tlie
pineal organ in tliis form was first mentioned by these authors
;ind Inter by Sorensen3"3 in 1894, who described the structure as
having a distinctly saccular form.

3. Amia calm. Goronowitsch ('88) 153 and Gage ('93). 135
Both of these authors showed that the pineal organ was a simple
sac in this species. Hill180 in 1894 found in the embryonic stages
evidences of both parietal organs, namely, what he calls the
anterior epiphysis and the posterior epiphysis which probably
corresponded to the parapineal and pineal organs in Petromyzon,
while the anterior epiphysis is considered the homologue of the
parietal eye in Saw' tans. In the later embryonic stages the
connection with the brain of the anterior sac is lost. Finally
the pineal organ is pushed to the left side. Eycleshymer112
found that the anterior organ has a lumen as late as the 15 to
16 nun. embryo. Nerve fibers were observed as late as the
12 to 13 mm. embryo going from the commissura habenularis to
the interior of the anterior organ. Kingsbury205 in 1897 observed
botli the pineal and parapineal organs in the adult Atnia. The
anterior organ was lying to the left of the pineal stalk and was
connected with the left habenular ganglion by means of a
thick, neural fasciculus.

4. J'oli/tidon folium. Garman ('90). 143 This species possessed
processes which look like nerve fibers. These processes go
from the iiitorbrain roof and extend out to an end-sac deeply
situated in a parietal fossa of the skull. In one case only was
there a complete parietal foramen.

5. 7W///>/r/-//.s hfchir. Waldschmidt ('87)'112

I). I'ali/iiicriix xctH'i/iiliiH. Waldschmidt.412 Both of these
species of ( Yossoptorygii present a pineal organ which has a
tubular stalk and rises above the dorsal sac. first upward, then
turns sharply forward to end in a slightly dilated end-vesicle.

THE PINEAL BODY 103

The walls of the organ have, in addition to the usual ependymal
cells, some special sensory cells. In the lumen are free cells with
no particular syncytial formation.

In the ganoids no mention is made of any evidence indicative
of glandular activity. Six ganoids in all have been carefully
studied and in only one, as already stated, are there signs of the
parapineal organ, namely, in Amia, otherwise all species present
a pineal organ which is not as well developed as in the selachians.

4- 'Comparative anatomy and histology of the epiphyseal complex

in teleosts

The epiphyseal complex in teleosts differs from that in selach-
ians and ganoids in its greater size. In some forms, however,
it is only rudimentary, being but a solid bud, while in others,
it is a complicated end-sac. It is never in any case like an eye
and seldom does it come into relation with the surface of the
head as in the cyclostomes. The number of species already
examined is perhaps too limited to make certain of all of these
observations. The only part of the epiphyseal complex which
develops and appears in the adult is the pineal organ. In a few
instances, during the very early stages of development, there
is present what may be considered the anlage of the parapineal
organ. The parts which the pineal organ presents in teleosts
are an end-vesicle, a stalk, and an ill-defined proximal portion.
In many instances the stalk is short and the end-sac large. In
most species the end-vesicle is pear-shaped and connected with
the roof by a hollow stalk. The walls of the end- vesicle are
either flat or formed into many folds, thus producing lateral
diverticula and giving the sac the appearance of a tubular gland.
In some cases the end-vesicle does not develop as such, the pineal
organ being a broad sac connected with the brain by a slightly
constricted area. The entire pineal organ may be a rudiment
as in Syngnathus, where it is almost solid throughout its entire
extent. The vast majority of the cells in the end- vesicle are
small and set closely together. Some cells have an epithelial
arrangement: these are doubtless neuroglia. The presence of

104

FREDERICK TILNEY AND LUTH10H !• . WARKK.N"

actual ganglionic cells is doubtful. Some cells observed by
Hillls" in 1894 have very long processes. Studnic-kn386 observed
that whatever the character of the cells of the end-vesicle may
be, whether special sensory or not, the entire organ is not a
gland. By this he does not deny the possibility that the struc-
ture may bo in part glandular. GaleottiM" in 1896 found some

.....Epid

Cor

• Po

Fiji. ~}\ The opiphyseal complex in Anguilla fluviatilis. according to Lcydifr,

L896.

I'., velum t rinisvcrsuiii; I)N., dors:tl sac; !'<>., pincnl organ: St., stalk.

<-vi(lcuce of secretory activity in the c<41s of the pineal organ in
tliese forms. In Lciicixcus, he observed nuclei which had fuch-
sinophile grannies and also nucleoli which later app-ared in the
protopla-in. The product, of this secretion was, in his opinion,
delivered to the lumen of the end-vesicle which is completely
surrounded by blood vessels. The stalk, when definitely pres-

THE PINEAL BODY

105

cut, has a form similar in character to the end-sac and is made
up, in the main, of small neuroglia cells. Nerve fibers constitut-
ing what has been called the pineal nerve of the stalk have been
observed making their way to the posterior commissure. Hill180
observed in Salmo purpuralus, and Studnicka386 in Cyprinus
carpio, Carassius aura'.us, Esox lucius, and Cobilis fossilis
what may be termed a tractus pinealis running from the pos-
terior commissure through the pars intercalaris posterior to the

.r-> L'r Epid

Sch

Fig. 55 The epiphyseal complex in Salmo purpuratus, according to Hill, 1894.

V., velum transversum; Ds., dorsal sac; Ch., commissura habenularis ; R.
proximal portion; P<>., pineal organ; Tp., tractus pinealis; Sch., pars intercalaris
posterior; Cp., posterior commissure.

stalk and then in the dorsal wall of the stalk to the end- vesicle.
Hill says these fibers are connected with elements in the latter
vesicle.

With reference to the site and relation of the pineal organ to
the skull, it has infrequently been observed that this organ
occupies a prefrontal fossa. What has been designated a
cornea, namely, a large mass of fiberless connective tissue above
the end-vesicle, has been described in teleosts, but there is no
parietal spot in any other form thus far investigated.

100 FREDERICK TILXKY AXD LUTHER F. \VARREN

Differences observed in the epi/thi/xeal coi///>lc.r in Utc mrious
species <>f tdeosts alrcadi/ investigated

PHYSOSTOMI

1. Kxi'.r ///r///.s. (iottsche ('3"))';i1 mentioned for the first time
the pineal organ in this form. Stieda378 in 1873 called it a red
body of very insignificant size. Cattie''° in 1SS2 distinguished
.-in end- vesicle and a stalk, the former richly supplied with
blood and deeply sunken into a fossa in the roof of the skull.
He described oval ependymal cells, and pear-shaped cells in
the end- vesicle. The stalk was hollow and its dorsal wall con-
tained a tractus pinealis. There were many folds in the end-
vesicle.

2. Tinea rnl'jaris. Cattie ('82).fi° In this form there is a
well-defined proximal portion, which, however, is a fine strand-
like structure. The end-vesicle is flattened and much expanded.

3. Sal mo salar. Cattie ('82).r'° This species has an end-
vesicle which is pear-shaped and a very short, highly vascular
stalk. The end-vesicle is in contact with the roof of the skull.

4. Salmo fario, pnrpuratus and fontinalis. Rabl-Riickhard
('83) ;319 Hill ('94).18° These forms present a pineal organ hav-
ing an end-vesicle in a depression of the skull and a stalk con-
necting it with the posterior commissure. The stalk has a cen-
tral canal, the lumen of which is bounded by cylindrical cells.
Hill found in embryos not only the pineal organ, but the para-
pineal organ as well; the latter remains rudimentary. Hill
called the pineal organ the posterior epiphysis. It presents a
proximal, narrow portion and a distal, flattened end-vesicle
which is thick and lodged in a deep fossa of the skull. It has
many diverticula and is rich in blood vessels. A long canal
runs through the stalk; nerve fibers connecting with sonic of
these cells in the end-vesicle make their way through a portion
of the stalk, and a definite tractus pinealis in the dorsal wall of
the stalk ends in the posterior commissure. In the adult of two
years old, Hill described a, distal end-sac which retains the em-
bryonic form. The rest disappears. In the distal part of the
BBC are many cell groups containing granular or colloid masses

THE PINEAL BODY 107

in irregular acini. The tractus pinealis persists. The anterior
epiphysis in the adult is reduced to a small mass of cells.

5. Anguilla fluviatilis. Cattie ('82). 60 In this species there
is a proximal portion and a cylindrical end-sac. Ley dig239 in
1896 described the end- vesicle as very much reduplicated and
highly vascular. Galeotti140 in 1896 saw a clear caryoplasm and
no granules or nucleoli in the end-vesicle. He, therefore, con-
cludes that there is no evidence of secretory activity in this
form.

6. Clupea alosa. Cattie ('82). 60 A strand-like stalk and an
expanded end-vesicle are observed in this form both of which
are solid.

7. Clupea . harengus. Holt ('91). 189 In the late larval stages,
the epiphysis in this species is a solid body. In younger em-
bryos a nerve bundle extends from the pars intercalaris up the
stalk. In the later stages there is a saccular epiphysis with a
wide lumen three or four cells deep. The lumen is filled with a
coagulum. The tractus pinealis is present in the dorsal wall of
the stalk.

8. Leuciscus rutilus. Rabl-Ruckhard ('83). 319 The distal end
of the organ in this form is flattened out against the inner
surface of the skull. There is a very thin but long stalk (fig. 56) .

9. Leuciscus cephalus. Galeotti ('96)14° found in the cells of
the pineal organ those above-mentioned structural peculiarities,
which he considered indications of secretory activity.

10. Amiurus catus. Ramsay Wright ('84).43° The pineal
organ in this species is tubular and has the same thickness
throughout its entire extent. It ends in a fatty tissue. Its
end-vesicle does not reach the cranial roof. Its walls are thin
and form no folds.

11. Callichthys asper and litioralis. Dean ('88). 81 In both
of these forms there is a parietal foramen with a retinoid tissue
lying beneath it. Klinckowstroem208 in 1893 found a parietal
foramen closed by connective tissue in these forms. An end-
vesicle was located here, but showed no particular specialization.

12. Doras, Clarias, Loricaria. Dean ('88). 81 In these species
there is a parietal foramen.

ION

FREDERICK TILXEY AND LUTHER F. WARREN

13. Coregonu* albus. Hill ('91). 179 In the embryonic state
of this species the anlagen of the pineal and parapineal organs
both occur.

14. ('(liaxli.trnis feres. Hill ('94)I8° found the anlagen of the
anterior and posterior epiphysis in embryos of this form. These
were almost transversely placed in relation to each other.

Kiii. •">(> Transverse sect ion t hroujili t lie end -vesicle of 1 lie pineal oruan in Leu-
riscus riitilus, according to Ralil-Riickhanl,
l'ii.. pineal or^ini; /////., lieiiiis|ilieres.

IT), ('ohm* ./V/.s-.s/V/.s and Imrh.iluhi. Studnicka ClMi).386 The
pineal oru,;in in these sp(H'ies is tubular. The distal (Mid forms a
lariie sac which lies beneath the skull. The tra.ctus pinealis is
present.

THE PINEAL BODY

109

16. Belone acns. Studnicka ('96).38i In this species there is
a long, tubular stalk. Ependymal cells form the walls of this
stalk and have an arrangement reminiscent of the retinal sen-
sory cells of the retina of Petromyzon especially of the region of
the large end- vesicle (fig. 57).

17. Cyprhius carpi o. Studnicka ('96). 383 The end-vesicle
in this form is a circumscribed dilatation and has a thin, hollow

•- Hm

Jlf

Cp R

Fig. 57 The epiphyseal complex in Belone acus, according to Studnicka, 1896.

Ls., lamina terminalis; Pf., paraphysis; D., dorsal sac; Ch., commissura ha-
benularis; R., proximal portion; Po., pineal organ; Cp., posterior commissure;
M., midbrain.

stalk, in the dorsal wall of which there courses the tractus
pinealis.

18. Carassius auratus. Studnicka ('96). 386 The pineal organ
in this form is tubular throughout its entire extent. There is a
tractus pinealis as usual in the stalk, but no fossa in the skull.

19. Argyropelecus hemigymnus. Handrick ('01). 168 In the
adult of this form both the pineal and parapineal organs appear
to be present. The pineal organ has a thin stalk and a large

110

i I;I:DKI;ICK TILXEY AXD LUTHER F. WARREX

end-vesicle which is much folded and highly vascular, being
mushroom in shape. This sac has much to suggest glandular
activity. Xo tract us i)inealis could be discovered in the stalk.
The end-vesicle lies beneath the roof in the frontal region and
there i- in this particular area an actual frontal or parietal fora-
men. The parapineal organ is tubular in form and lies in front

------- Po

."s ( 'ross section of pineal or^an :m<l
nus. acconlinji to 1 landrick, I'.IOl.
])s., dorsal sac; /'" . pineal oru;aii.

sac in Aiuyropelecus

of the pineal organ. Il is shorter than the pineal organ and does
not reach the parietal foramen. It has a lonu -talk. Stud-
nicka:; thinks Haiidrick's para])ineal organ is not hing more than
a peculiar forina,t ion of the dorsal sac.

•_'(). < I/Minus. Tei-ry ('Hi. The piiu-al organ in this species
pre-eiits an o\-al end-\-<->icle with a long slender stalk, both of

THE PINEAL BODY

111

which contain a lumen, but neither have connection with the
third ventricle. The cavity of the pineal organ is traversed by
protoplasmic processes forming a dense meshwork from wall to
wall. Although the pineal organ is highly vascular in Opsanus,
it does not conform in structure to any of the known ductless
glands, and is, therefore, probably not glandular. There is no
pineal nerve, no parietal foramen or fossa, no dorsal sac or
paraphysis.

PV

PC V

Fig. 59 Pineal region in an embryo of Opsanus, according to Terry, 1911.

T.R... lamina terminalis; P., paraphysis; V., velum trans versum ; P.V., post-
velar arch (dorsal sac); S., commissura habenularis; E., epiphysis; P.C., pos-
terior commissure.

PHYSOCLYSTI

21. Gadus morrhua. Baudelot (70). 14 The pineal organ in
this species is a long, pear-shaped structure. Cattle"0 in 1882
distinguishes a strand-like proximal portion and an end-vesicle
rich in blood vessels. In the latter are round and oval nuclei
and round and pear-shaped cells with one or two processes.

22. Trigla liirundo. Ussow ('82).40: A short pineal organ
with a hollow end-stalk is the characteristic in this species.
The end-vesicle is convoluted and reminiscent of the conditions
in the hypophysis. The cells bordering upon the lumen are
ciliated while the parenchymal cells are probably neuroglia.

112 FREDERICK TILXKV AM) U'THER F. WARREN

23. Cycl<>i>li-ru* lumpus. Cat lie ('82). 60 In this form the
pineal organ is only rudimentary, being made up of a short,
conical body representing the stalk, while the distal part is
entirely absent.

24. Lulu rulyari*. Cattie ('82). 60 As in Gadus, the end-
vesicle in this species lies against the roof of the skull. The cells
in this vesicle are similar to those in Gadus.

25. I*leiir<ntcctcs platessa. Cattie ('82). 60 In this species the
stalk is solid and so also is the end-vesicle. The latter is highly
vascular and the stalk is very long.

2(). Lucioperca vitrea. Hill ('94).18° In this species the
anlagen of both the parapineal organ and the pineal organ
appear.

27. Loplifiis piscatorius. Studnicka ('96). 386 An end-vesicle
and a stalk are present in this form. The end-vesicle is in a
deep fossa. There are two types of cells in it besides the epen-
dymal layer, namely, neuroglia cells and sensory cells. Nerve
fibers were observed in the stalk.

28. Cepola rubescens. Studnicka ('96). 386 A thin stalk with
an expanded end-vesicle sharply flexed forward is the charac-
teristic in this species. The lumen in both is conspicuous. The
end-vesicle is much convoluted and rests against the roof of
the skull.

29. Anarrhirhux ////;//*. Studnicka ('96).38fi In this form
1 here is a very long stalk, but no recognizable end-vesicle. There
is a tract us pinealis in the dorsal wall of the stalk and a plasmatic
lens in its lumen.

MO. Ophidiiun. Ixirlxitnin. Studnicka ('96).38ti In this species
there is a thin, long, hollow stalk and a very small but elongated
end-vesicle. There is no fossa in the skull and no tract us
pinealis, but many blood vessels accompany the stalk as far as
the end-vesicle.

.'il. Arnoglossus lanterna. Studnicka ('96). 886 In this species
there is a hollow and long stalk with a well-marked (Mid-vesicle.
Thi> ve>ic]e is vascular, but is situated in a position far removed
fnun the skull roof.

THE PINEAL BODY 113

LOPHOBRANCHII

32. Syngnathus acus. Studnicka ('96). 386 The pineal organ
in this species is rudimentary, only the proximal portion of it
being present. In this there is a small lumen.

33. Hippocampus spinosus. Studnicka ('96). 336 The pineal
organ in this form is a small, short sprout, the distal end of which
does not reach the roof.

In all, thirty-three species of teleosts have been investigated.
Of these, thirty species present a more or less well-developed
pineal organ. In one form it is almost entirely absent present-
ing itself only as an inconspicuous rudiment. This is the case
in Syngnathus acus. In a second instance, Hippocampus
spinosus, the pineal organ is little more than a short sprout. In
five instances among the teleosts both pineal and parapineal
organs appear, the latter occurring either in the adult, which
is rare, or during the earlier stages of development. Both
organs appear in the anlagen in Coregonus albus, Lucioperca
vitrea, and Catostomus teres, but later disappear in these forms.
Both organs are well marked in anlagen and remain as discern-
ible rudiments in Salmo purpuratus and fario and also in Argyro-
pelecus hemigymnus. In one instance, Leuciscus cephalus,
there was definite evidence of secretory activity in the pineal
organ. In three species there was evidence of a retina in the
pineal organ, either because of the presence of specialized sensory
cells or of nerve fibers coming into connection with these cells.
In three instances there was a distinct parietal foramen. It is
significant in this connection to note that in no instance in
which there was a retinal-like structure or cellular formation
and arrangement suggestive of a retina, did there occur a parietal
foramen. In seven cases the end- vesicle of the pineal organ was
lodged in a fossa on the under surface of the skull. In seven
species, namely, Cobilis fossilis and barbatula, Lophius pisca-
torius, Cyprinus carpio, Carassius auratus, Anarrhichas lupus,
Pleuronectes platessa, and Clupea harengus, there is evidence
of a nervus pinealis or a tractus pinealis. All of these descrip-
tions except one are given by Studnicka.386 This observer makes
the statement that there is no nervus pinealis in Ophidium
barbatum.

MEMOIR NO. 9

114

FREDERICK TILXEV AXD LUTHER F. WARREN

5. Comparative

n/nl hixtolotji/ of the epiphyseal complex

in tun /tliihid

In aini)liil)i:i the pineal organ alone makes its appearance.
In no other form is this organ so little developed. It presents a
small end-vesicle which Stieda'7'' first recognized and described
as the frontal xuhctihun'oux (/land. This end-vesicle is attached
by means of a thread-like strand to a considerably expanded
proximal portion, to which latter the name of epiphysis or corpus
pineale has been ascribed. The pineal organ consists, there-

Fig. GO Head of Kana temporaria showing the unpaired pineal eye, situated
the paired eyes, according to Stieda, 1865.

fore, of the usual parts, namely, an end-vesicle, a stalk, and a
proximal portion which is particularly conspicuous in amphibia,.
The end-vesicle in so far as is known, is present in all forms
except If i/l(i arborea, the absence in this form being noted both
by de( Iraat',1" and Leydig.-:is In shape, the end-vesicle is round.
oval, or kidney-shaped. Stieda17'' and dedraaf1" found it solid,
containing a lumen only in Ijoinf>in<ilor. According to Stieda.
its diameters ace from .12 to .1") mm. dedraaf found these
diameters in l\<in<t esculenta from .\'2(\ to .14") mm., while
Lessona-11 in the forms studied by him found that t lie diameter
was less than 1 mm. A number of observers, including Ostrou-
moff2" ('87); Lcydig^ ('91) ; Galeotti140 ('96), and Braem" ('US),

THE PINEAL BODY

115

maintain that the frontal organ contains a cavity. According
to Leydig, this organ contains pigment in Bombinator, but
otherwise, in frogs, the cells are pigment-free. Histologically,
the cellular elements of the frontal organ show no definite
arrangement. These cells are usually long and their mass
is traversed by a few isolated fibers. deGraaf and Leydig both
found evidence of fatty degeneration in the organ. The so-
called frontal subcutaneous gland of Stieda is situated, as de-
scribed by that author, directly under the corium of the skin

Po

EpiJ

M

Pf V Ds Ch

Fig. 61 The epiphyseal complex in the pineal region of Rana temporaria, ac-
cording to Braem, 1898.

Ls., lamina terminalis; Pf., paraphysis; V., velum transversum; Ds., dorsal
sac; Po., pineal organ; N .pin., pineal nerve; Ch., commissura habenularis; Ep.,
proximal portion; Cp., posterior commissure; M.. midbrain.

in the midline of the head and upon a transverse line from pupil
to pupil. According to Lessona,241 its position is marked by a
clear, white spot on the top of the head, not well developed in
all forms, but first described by Stieda375 as the Scheitelfleck or
parietal spot. According to Leydig,238 this spot is best made
out in Rana arvalis and agilis. It also occurs in Rana esculenta.
The stalk of the pineal organ in amphibia exists as a thin,
strand-like structure. Stieda375 in 1865 first referred to it as
a thread connecting the frontal gland with the skull. Ciaccio65
in 1867 recognized the nerve fibers in this strand. Lessona241 in
1880, deGraaf155 in 1886, and Leydig238 in 1891, all observed the
nerve fasciculus in older animals, but did not appreciate its
significance. They thought it to be the remnant of the connect-

116 FREDERICK TILNEY AND LUTHER F. WARREN

ing strand between the attached and detached parts of the
pineal organ, thus represent ing a degenerative process. Braem39
in 1898 also found this fasciculus and made the further observa-
tion that it contained heavily myelinized nerve fibers. He
likewise was of the opinion that there was evidence of degenera-
tion in this nerve fasciculus, in this way confirming the view of
deGraaf and Leydig. Haller16''1 in 1898 stated that the fibers of
the tractus pinealis spring from two branches of roots connected
with the thalamus ventromedial to the commissura posterior.
Gaupp147 in 1898, who first applied the term of tractus pinealis
to these fibers, observed fine nerve bundles passing in the ventral
portion of the epiphyseal stalk. Most observers believe that
these fibers come into relation with the posterior commissure.
The proximal portion of the pineal organ. This, as already
stated, was known as the epiphysis or corpus pineale. It was
also called by Gaupp147 in 1898 the pediculus corporis pinealis.
Osborn288 in 1884 described it as a cylindrical, hollow, anteriorly
flexed sac whose lumen was in communication with the third
ventricle. Rabl-Riickhard317 in 1880 states that the proximal
portion is solid. Osborn, on cross section, described it as
round. Gaupp147 and Braem39 state that the organ lias an
elliptical form with many short diverticula which give it a
glandular appearance. In this feature it is like some teleosts,
reptiles, and birds. Galeotti140 in 1890 found evidence of secre-
tory activity in Rufo and Rand, for example, granules in the
cytoplasm staining with acid fuchsin. Studnicka386 in 1890 saw
the same appearances in adult animals which he thought were
sensory cells and which he likened to the sense cells in the pineal
organ in Pctron/i/zon. Ostroumoff-91 in 1887 found fine fibers
between these cells.

Differences observed in the epi plujxcal complex of the various

species of aniphihia

URODELA

1. A-nihli/xlnmti incxicanum. Stieda (75).379 In this form the
chorioid plexus was first mistaken for the epiphysis. Orr2S15 in

THE PINEAL BODY 117

1889 first discovered the pineal organ in embryos. Eycles-
hymer112 in 1892 made a more extensive study of this organ and
found the epiphysis to be a long, glove-finger shaped struct-
ure. The cells in the under wall were somewhat larger than
those in the upper wall and some of them contained pigment.

2. Amphiuma means. Osborn ('83). 287 In this species there
is a marked plexiform paraphysis, while the pineal organ extends
forward as a small sac over the commissura habenularis.

3. Menopoma atteghaniense. Osborn ('84). 288 The pineal
organ in this species is a saccular evagination with a lumen
opening into the third ventricle.

4. Menobranchus. Osborn ('84). 288 In this form the pineal
organ is a long, flattened sac completely detached from the
brain. Kingsbury204 in 1895 showed that there is a well-marked
paraphysis and also that there are nerve fibers in connection
with the pineal organ.

5. Salamandra maculosa. Burckhardt ('91). 43 The pineal
organ in this species is a short, hollow, and rudimentary stalk.
There is a flattened end-vesicle in which there appears evidences
of degeneration.

6. Diemyctylus viridescens. Gage ('93). 135 The pineal organ
in this form is very small in the adult and there is no lumen in
any portion of it, There is, however, a well-developed para-
physis.

7. Desmognathus fuca. Fish ('95). m The pineal organ in
this species is a small compressed structure. It contains no
lumen in the adult, but in the larva the organ is hollow.

8. Triton taeniatus, cristatus and alpesiris. deGraaf ('86)15S
The pineal organ in these species is rudimentary. There is a
short, hollow stalk and a flattened end-sac in which there is
evidence of a process of degeneration. This same form was
studied by Blanc34 in 1900 with practically the same results.

9. Spelerpes fuscus. Galeotti ('96).14° In this species the
pineal organ is oval and hollow. The end-sac is directly in
connection with the commissura habenularis and there is no
stalk. The cells have an epithelial arrangement and are formed
in alveoli, giving the structure a glandular appearance.

IIS FREDERICK TILXKV AM) LUTHER F. WARREN

10. 1'rolcnx anyiiinnx. (laleotti ( '(.H'»).I4° The pineal organ
in tliis form is small and pyrifonn and has no evidence of
srrivtory function.

11. Salattia/nlrina perspicillata. Galeotti ('1)6. 14° In this
species the pineal organ is a small, flattened structure.

. \roi)A.

1. Ichllii/(>i>hix (jlni'masa. Burckhardt('90).42 The pineal organ
in this form is small and pyrifonn and has a short stalk, but
does not reach the skull roof. A well-developed paraphysis is
present. Fibers from the end- vesicle seem to make their way to
the commissura habenularis.

AXURA

1. liana rxculrnld. Leydig ('68) ,233 In this species the end-
vesicle has a figure-of-eight shape and is solid. Leydig238 later in
1891, could find no evidence of a parietal spot in liana ./'//.sea.
de(lraafir>:' in 1886 found a well marked end-vesicle which was
solid and round and a well-developed parietal spot.

2. Cei'<ita/>liri/x. Lessona ('80). -11 There is a fairly well-
marked end-vesicle in this species.

3. Bufo cineretix. Lessona ('SO)241 did not observe a pineal
organ in this form, but it was found subsequently by de( Iraaf1 •'•''
in issii. Sludnicka386 also found it in young larva-.

4. J'dolxilrx ///.ST//.S. Lessona ('SO)'-'41 found the end-vesicle
in this species.

f). />/.sn;///n.s-.s//.s. Lessona ('80). 2" A fairly well-marked end-
vesicle exists in this species.

6. .l////rx nfixlrlriranx. Lessona ('SO).'-'" In this form there
is a well-marked end- vesicle which was first accurately described
by de( iraaf.'"'1

7. liana <><•<•/ />/i<tl /* and fiyrina. Lessona ('SO).'" In these
forms the pineal organ presents a well-marked end-vesicle.

8. rina antcrii-ana. f.essona ('SO).-'" In this species thei'e
is no end-vesicle.

'.). ll,,la arborea. dcdraaf (J86),1M and Leydig ('91)Ma both
found thai llx- end-\'esicle was absent and that the skin in the
usual position of the parietal spot showed nothing of the existence
of such ;i -t met lire.

THE PINEAL BODY 119

10. Bombinator -igneus. Leydig ('68) ;233 deGraaf ('86). 155 In
this species the end-vesicle is saccular.

In the twenty-two species of amphibia investigated, the great
majority present a well-developed paraphysis. In but a single
well-defined instance is there evidence of a tendency toward the
formation of a retina. This occurs in Amblystoma mexicanum
in which there is evidence of pigment formation in some of the
cells of the end-vesicle. In several forms the stalk contained
fibers suggestive of the pineal nerve. With reference to the
possible glandular character of the organ it must be borne in
mind that Stieda's379 original description referred to the struc-
ture as the frontal subcutaneous gland. The general arrange-
ment of the cells, both in the end- vesicle and in the proximal
portion, has epithelial masses which tend to lend weight to the
view that the organ may have secretory function. In only one
instance, however, that is in Spelerpes fuscus, has there been
observed any definite evidence of glandular activity in the
pineal organ.

6. Comparative anatomy and histology of the epiphyseal complex

in Reptilia

In considering the conditions present in the epiphyseal com-
plex of reptilia, two groups of these animals must be distin-
guished. The first group is that comprising the more ancient
reptiles, e.g., the saurians and also the prosaurians as represented
by Sphenodon. In the second group are the reptiles of more
recent history, including ophidians, chelonians and crocodilians.
It is in the first group, however, that the most striking appear-
ances are observed in the epiphyseal complex. In these forms
there develops a structure so remarkable for the many features
which identify it as a visual organ that the term parietal or
third eye by which it has been designated seems altogether justi-
fied. Quite as striking in a negative way, on the other hand,
are the conditions in the ophidians and in the chelonians where
this eye not only altogether fails, but there is no evidence
whatever of a parapineal organ either in adult forms or in
the anlage, while the pineal organ also shows marked regressive

120

FREDERICK T1LXHV AND LUTHER F. WARREN

alterations in the loss of several of its parts as compared with the
lower forms already considered. Finally the reported absence
of any epiphy-ea! structures whatsoever in crocodilia offers much
room for speculation or, perhaps, serves as an incentive to rein-
vest Ration.

The pineal on/an in saurians and prosaurians (form Sphenodon]
seldom presents all three of the several parts usually observed
in the pineal organ, and it is not possible to identify an end-

-Hm

. (>'2 'I'li<' cpiphyscal complex in Sphcnuxlon according fo Spencer, 1SS<>.
I'n., p:ii';ipinc:il organ icnd-vrsicio i ; /'/., parapliysis ; I)*., dorsal sac; I'.'/i.,
proximal portion of pineal organ; .I/., midbrain.

vesicle, a stalk, or a proximal portion. Often the end-vesicle is
absent, and in no instance does it assume the proportions or
the characteristics of a visual organ. The stalk is usually
hollow, but contains no nerve fibers, and in the instances in which
the end-vesicle is absent, the stalk is drawn out into a tapering
process or end-tube. Melchers-'1'-' in IX1.)',) showed that not only
may the eiid-s.-'c be absent, but the rest of the parapineal organ
may pivM-nt itself in a degenerative condition. This is true in

THE PINEAL BODY 121

Platydactylus. In some cases, as in Gehyra oceanica and
Hemidaciylus mabouia, described by Stemmler374 in 1900, the
entire epiphyseal complex may be only recognized in the slightest
rudiment possible. In one instance reported by Studnicka,386
namely, Pseudopus pallasi, there is an end- vesicle, a stalk, and
a proximal portion. The stalk is, in fact, a double one, or, in
other words, there is a main stalk and a secondary accessory
connection between the end-vesicle and the roof-plate of the
brain.

The proximal portion of the pineal organ, known as the epi-
physis or corpus pineale, is present in all forms. In some cases
the proximal portion is a simple pyriform structure attached by
a thin stalk to the roof of the interbrain. In other instances it
is spindle-shaped or oval. The walls of the proximal portion
are thick and usually flat inside as well as outside. In some
cases there are inner reduplications, as in the fish. Leydig238
in 1891 found thick accessory spaces in the organ of Lacier a
ocellaia and Anguis frag His due to septal formation. The wall
may be much folded, giving the appearance of a complicated
glandular structure. Edinger105 in 1890 showed this in one of
his cuts (fig. 63).

The histological structure of the pineal organ. The chief cellular
constituent of the pineal organ, both in its end-vesicle when
present and in the proximal portion, is the ependymal cell.
Neuroglia cells also occur interspersed among the ependymal
elements, but there are no ganglionic cells. Nerve fibers lie
parallel with the outer dorsal surface quite similar to the nerve
fibers in other pineal organs. These are probably the nerve
fibers which constitute the tractus pinealis. Klinckowstroem207
in 1893 found cilia on the cells of the pineal organ in embryos
of Iguana and Tejus, but not in the adults of these species.
Pigmentation is either entirely absent in all parts of the pineal
organ or when present it is in the interior of the cylindrical
cells placed in the lumen. A tractus pinealis was described by
Leydig239 in 1896 in Platydactylus. Melchers, however,269 in 1899,
showed these fibers were probably connective tissue. Saurians,
as a rule, although they do not in every case present a well-

l'J_ FKKDKKICK TII.NKV AM) LI THKK F. WAKKKX

marked tract us pinealis, nevertheless in a certain number of
instance- a nerve tract may be observed connecting the pineal
organ with the roof of the interbrain.

/// ()/>hi(/iti the pineal organ is rudimentary. Only the prox-
imal portion persists in the snakes. This, however, has under-
gone considerable modificat ion from the proximal portion already
encountered in the lower vertebrates. In the true snakes it is
a compact, highly vascular structure to which the term epiphysis
or corpus pineale may, in the strict sense, be applied. Hoff-

Cor

Fig. <>:{ The opiplivx'.-il complex in Annuls frntfilis, according to
L891.

/'.".. p:ir:i|)iiii-:il nr^.-in; l'l\>.. pnixiiiuil port inn of pineal or.nan.

jnannls'; in isxii showed that tlu^ corpus pineale in ophidia begins
in its development as a simple evagination from the intcrbrain
roof. How it a.ttains its later complicated, compact form is not
yet exactly known. Xo doubt the solid epiphysis due to the
proliferation of the wall of the anlage causes the obliteration of
the lumen of the original evagination. A paraphysis develops
<-;irly in ophidians and has in its inception the same general form
as t he epiphysis. The pineal region in the adult consists, t here-
fore. of ;« p.-iraphysis which is a thick-walled structure associated
with i he chorioid plexus, a velum I ransversiim and a, dorsal sac

THE PINEAL BODY 123

also complicated in the chorioid plexus, acommissura habenularis,
an epiphysis with a fairly well marked recessus pinealis and a
posterior commissure. Herrick177 in 1891 described the epi-
physis in ophidia as a compact, somewhat rounded or oval
body whose interior consists of a connective tissue network with
many blood vessels, thus giving it the appearance of a branched,
tubular gland. Studnicka386 maintains that nothing definite is
known of the significance of the epiphysis in snakes. Its un-
usually rich capillary blood supply speaks in favor of the sup-
position that the organ is a gland which contributes its product
to the blood stream.

In Chelonia the pineal organ is only in a rudimentary condi-
tion and develops in these forms an epiphysis or corpus pineale.
Just as in ophidians, the end-vesicle and the stalk of the pineal
organ appear not to be laid down in anlage, or if it does occur in
the early stages of the development, it soon disappears, leaving
only the proximal portion to represent the pineal organ in these
forms. Neither in chelonia nor in ophidia is there any evidence
of an anterior epiphysis, that is to say, a parietal eye. The
first description of turtles was given by Bojanus36 in 1819.
Tiedemann395 also mentioned the epiphysis in turtles, but prob-
ably mistook the chorioid plexus for that structure. Voeltz-
kow410 in 1903, describing the embryology of Chelone imbricata,
mentions the first appearance of the epiphysis as a simple evagi-
nation. Secondarily, a stalk develops between the pineal organ
and the roof of the interbrain, so that, according to Voeltzkow,
the epiphysis in Chelone imbricata separates itself entirely from
the roof-plate. The pineal region in chelonia presents the
usual features, namely, a large paraphysis which forms an
unusually extensive sac. The end of this sac lies directly over
the epiphysis. The velum transversum and dorsal sac are
incorporated in the chorioid plexus. There is a fairly well
marked commissura habenularis, the epiphysis in its usual
chelonial form, and also the posterior commissure. The form
of the epiphysis in the turtle is oval or ovoid; it lies close to
the roof-plate. The surface, as Herrick177 has shown in 1891,
is uneven and may indicate r, process of lobulation. Many

124 FREDERICK TILNEY AXI) LUTHER F. WARREN

trabeculae of connective tissue extend inward toward the center
of the organ from the capsule. The cellular elements are for
the most part ependymal cells and neuroglia. No ganglionic
cells and no nerve fibers were observed. There is no clear
evidence of secretory function in the epiphysis of Chelonia. The
organ contains a small cavity.

/// Crocodilia, the pineal organ, according to Sorensen ('94), 363
as well as the other elements of the epiphyseal complex, is en-
tirely absent. In the roof of the interbrain there is a well
marked coimnissura habenularis and a posterior commissure
with possibly a dorsal sac and a paraphysis. Voeltzkow410 in
1903 found no epiphysis in Crocodilus madagascariensis. Rabl-
lUickhard3"5 in 1878 showed in Alligator mississippiensis a
long, rounded conarium. This observation, according to later
observers, is probably an error, the paraphysis and chorioid
plexus having been mistaken for the pineal body.

The parietal eye in Re pt ilia. The parapineal element in
saurians and sphenodon gives rise to what is known as the
third or parietal eye of reptiles. Among the saurians it is not
universally present. Its absence has been noted in certain of
the Geckonidae, as for example, Hemidactylus, Gchyra, Gecko,
and Platydactylus. It is also absent in certain Agamidae, such
as Draco, C&ratophora, Lyriocephahis, and Moloch. It has not
been observed in Tejus and Cy clod us. The general form of the
parietal eye is saccular with the upper wall corresponding to a
lens which is pigment free wrhile the under or ventral wall which
corresponds to the retina is deeply pigmented. The third eye
presents several different forms in the different species:

1. It may be pyriform, as is the case in S^hcnodun, Spencer366
and Ley dig, '-'•'"' and Iguana, Spencer.3'17 It is also of this shape in

iH'buloxux and An(/uis, Hanitsch,169 also in Pseudopus
/, Studnicka.:ts';

2. Dorsoventrally elongated and ovoid as in Annlix and
Lyriocephalus, Spencer.™7

3. Spherical or hemispherical, in which latter case the lens is
flattened, as in Lticcrla occllulti, Chameleon, Grammatophora
liarlialii, Moloch horridnx, and Agania l//x/>/<l<i, I,eydig'-':: and
Spencer.

THE PINEAL BODY

125

4. Lenticular and flattened, as in Anguis fragilis, Lacerta
vivipara, Lacerta agilis, Lacerta viridis, Seps tridactylus, Varanus
giganteus, Plica, Iguana, and Calotes.

5. Flattened so that the under wall is pressed inward,
as in Varanus bengalensis, Leiolaemus mtidus, and Calotes
ophiomachus.

6. Flattened and decidedly elongated, as in Seps chalcidica
and Calotes versicolor.

Fig. 64 The pineal eye of Anolis, according to Spencer, 1886

While the dorsal wall of the parapineal vesicle forms the true
lens of the parietal eye, the ventral wall is pigmented and gives
rise to the retina. The latter consists of layers of different
types of cells. In the embryonic stages it is attached to the
brain by a tubular prolongation from the roof-plate. The first
detailed description of the parietal or third eye in reptiles was
given by deGraaf155 in 1886. Spencer's366 work appeared in
the same year, and a number of investigations have been reported
since then confirming in a general way the conclusions of these

120

FKKDKHirK TILXKV AND U THER F. WAKIM.X

early worker-. These researches include those of Beranock
('87)-' in AtHjuix and Lncertn; Franc-otto ('S7)127 in AtKjni*;
McKay ('88)'->;'" in Grammatophora and Hinnlid; Strahl and
Martin ('88)383 in Lucnia, and Hitter ('91)332 in Phnjin^nini.
There is a general agreement regarding the histological structure
of the retina among saiirians, and the following layers have
been identified by most of the investigators mentioned:

Fi><;. '••") The structure of the retina in the pineal eye in Sphcnodon punrtatum
accordiiiK to Spencer, 1886.

1. Aii inner layer of long, cylindrical cells, called the rods or
rod-like bodies of Spencer366 or the cellule* (xilonncts of Fran-
cotte.1-7 In these cells pigment occurs.

'_'. An inner layer of cells, called the 'couche cellulaire interne'
by l''raiicotte.127 This consists of round cells with a large round
nuclei. Ritler'-'1'-' distinguishes 1\vo types of nuclei in this layer,
najnol}r, those which are round and small and those which are
oval and long.

THE PINEAL BODY

127

3. A molecular layer described by Spencer366 and Francotte127
or a layer of nerve fibers described by Strahl and Martin.383
The latter observers and Klinckowstroem206 maintain that these
fibers are in connection with the parietal nerve. Leydig238 and
Dendy86 believed that a cleft occurred in this layer which, ac-
cording to Leydig, gives rise to a lymph space.

4. An outer cellular layer of round cells somewhat deeper than
the second layer.

5. A membrana limitans externa.

Fig. 66 The pineal eye in Iguana tuberculata, according to Klinckowstroem,
1894.

The most important elements in the retina are the rod cells
which appear to correspond to the ependymal cells of the retina
in the pineal organ of Petromyzon. They are long, cylindrical
elements in \vhich may be differentiated an outer thread-like
part and a more cylindrical portion. The nucleus occupies an
enlargement in the area of transition between these two por-
tions. The inner cylindrical parts lie close together; the outer
thread-like parts have broad spaces between them in which
are lodged neuroglia and some ganglionic cells. The peripheral
processes come to the surface of the retina and spread out against

ll'S FREDERICK T1LNEY AND LVTIIKK K. WARREN

the membrana limitans externa. The pigment in the cells is in
some cases arranged in transverse hands or stripes, according
1o Spencer361 in X/>h< no<l»n and Leydig ('91),--'^ in J//r////.y. All
of the rod cells are similar. The connection of the retinal ele-
ments with fibers of the parietal nerve is not yet altogether
understood. In adults the organ is rudimentary. It is not
known whether the nerve fibers come from the large retinal
elements, from the ganglionic cells of the deep retinal layer, or
from the large cylindrical cells of the inner layer. The latter
seems most probable in view of the conditions in Pctr<>itii/z<>n.

Tin /mn'cldl ncrrt'. This nerve was first described by Spencer366
in 1886 and has been observed by many others since then.
Spencer believes that the parietal nerve is connected with the
end of the epiphysis, that is to say, a direct continuation of the
pineal organ. The entire course of the parietal nerve from the
parietal eye to the brain roof was first traced by Strahl and
Martin3S3 in 1888 in older embryos of Lacn-ln r/ri/xir<i and
Anyiiix //v/f////.s. These observers showed that the nerve was
completely independent of the epiphysis. Beraneck23 in 1892
made more exact studies and confirmed the view of Strahl and
Martin. Other authors are also emphatic in stating the com-
plete independence between the epiphysis and the parietal eye.
Among them are Studnicka ('93), 384 in Luccrlu; Klinckowstroem
('94)20'-' in Iguana; Leydig ('96)239 and Dendy ('99) " in Spheno-
don, and Schauinsland f()3)347A also in Xplicinxlon. The parietal
nerve begins to develop shortly after the separation from the
roof of the parietal eye. Of the direction of its fibers, whether
from the brain to the eye or, as is the case in the pineal organ
and the paired eyes, from the eye to the brain, there is no proof.
The latter course, however, is most probable. In An</ui*, the
parietal nerve first appears at 50 mm. embryo size and reaches
its maximum of development between the '27 and 30 mm. si/e.
In ft/iifi //<i, the nerve is well developed at fourteen days and is
at its maximum at twenty-four to twenty-six days. Between
the thirtieth and fortieth days it shows signs of reduction.
Strahl and Martin;vi showed that the nerve comes into relation
with the ganglionic cells forming a prominence with the brain

THE PINEAL BODY

129

roof. This Beraneck23 designated in 1892 as the noyau parietal.
The prominence thus described can be nothing else than the
closely set ganglia habenulae of the interbrain as shown by
Studnicka384 in 1893 in Lacerta, by Klinckowstroem209 in 1894
in Iguana, and by Leydig239 in 1896 in Lacena. The parietal
nerve is made up of fine fibrils; it has a perineurium, a connec-

\ fur

Fig. 67 The pineal eye of Varanus giganteus, according to Spencer, 1886.
Pa., parapineal organ; Npar., parapineal nerve; Bl., blood vessel.

tive tissue, and glial sheaths. In Iguana it degenerates and
disappears in the adults, according to Klinckowstroem ('94). 209
In some cases Spencer366 found the parietal nerve divided into
two or three strands, for example, in Lacerta ocellata and
Varanus giganteus. A similar splitting was found by Studnicka384
in 1893 in Petromyzon. Klinckowstroem209 in Iguana recognized
a second parietal nerve which arose from the left habenular

MEMOIR NO. 9

V

130 i I;KDERICK TILNK.V AND LI TIIKK r. WAKKKX

ganglion niul passed close behind the first nerve to the parietal
eye. The lens of the parietal eye is not uniform in its shape;
it occurs in the following different forms:

1. Regular bi-concave lens, both surfaces curved, which is
most common in Lacc/in r/npara, Laccrln ugHi* and Lnariu
L< iulm max ///tiilus, Scps cJiiilciilica. Phrynosoma d»ng-
and Sphenodon.

'2. Bi-convex, with the under surface more convexed than the
upper, as in Anolfs and Sphenodon.

3. Plano-convex, as in Anyni* and Iginunt.

1. ( 'oncavo-convex, as in Calotes, Vannm* l><//</altns/x, and
}', i run us (lit/tuilcHS.

'I'lie structure of the lens is ma.de up of peculiar, long, cylin-
drical cells apparently derived from modified ependymal cells.
These are the so-called lens cells. There are some intercellular
spaces, probably lymph spaces, according to Leydig ('91). 23
The lens cells are nearly free of pigment. The substance of these
cells is very hard. Their nuclei are oval or round and are sel-
dom scattered over the entire lens surface or its entire thick-
ness. They are most numerous at the border of the lens where
the latter passes over into the retina.

The parietal foramen. Ley dig" in 1872 found a round or oval
opening in the skull of N/,7/."//m/r>// situated in the osparietal,
which seemed eil her directly to serve as the outlet for the parietal
organ or else for the entrance of light rays. It was reminiscent
of a similar opening in the cartilaginous roof of the cranium in
selachians. In most cases the parietal eye is in, or directly
under, this foramen. Species which do not possess a parietal
eye have a parietal foramen which is filled by the pineal organ,
in which ca.se, the end-vesicle takes the place of a third eye as
far as location is concerned. The foramen is absent in a large
number of saurians, particularly in the ( ieckonidae, and it is
also absent in ('crato/ilmni UX/H r<i. There are also instances in
which the foramen does actually appear in some individuals of a
species and yet in other individuals of the same -.pecies it is closed
by bone. The eye usually lies in the middle of this foramen or
near its upper edge. The relation be! \\een eye and foramen is

THE PINEAL BODY 131

different in different periods of life. The foramen is not the
result of direct pressure of the eye, but occurs for the purpose of
permitting the passage of light rays. As a rule, the parietal eye
lies in the foramen or under it, so that its optic axis corresponds
to that of the foramen. In Sphenodon a single exception to
this rule is noted by Spencer.306 Here the organ is tipped for-
ward so that the light rays cannot reach the entire retina. The
size of the foramen differs and bears no direct relation to the
size of the parietal eye. The third eye is connected to the
foramen by means of connective tissue and is surrounded by
lymph spaces while blood vessels make up a net about the
edges of the foramen. No mention of muscular tissue or dis-
crete muscles has been made in connection with the parietal
eye.

Leydig238 in 1891 found in Lacerta muralis, near the tip of
the epiphysis, four round, free, calcium bodies. Similarly in
Varanus nebulosus many small pieces of calcium carbonate have
been observed. These, however, have nothing to do with the
more common deposits of brain sand in the pineal organ of
mammals, as Leydig238 originally thought.

The interior of the parietal eye contains a coagulum, the
vitreous or the corpus vitreum. This consists of a syncytial
layer of cells entirely free of pigment. A sclera has been de-
scribed as developing in connection with the membrana limitans
externa which passes over into the connective-tissue sheath of
the eye. There is a space between these two layers which was
originally supposed by Leydig238 to be a large lymph space. In
most cases the connective tissue forms a sheath for the eye
which may be considered as a sclera. In other instances it is
absent. The connective-tissue capsule of the parietal eye is
considered analogous to the sheath of the eye in Petromyzon.
The connective tissue above the eye becomes differentiated as a
cornea and contains no pigment. It is almost fiberless connective
tissue. A parietal spot is absent in those saurians in which
no parietal eye or no parietal foramen develops. It is recognized
as a less pigmented area in the skin and presents many different
appearances, as well as differences in size, in the several species
of saurians (fig. 68).

132

FREDERICK TILXEY AND LUTHER F. WARREN

Accessor// />/>/«il a/nl /><ir<i/>///«il <>r</<inx in Rep tili a. A number
of observers have reported the appearance of accessory struc-
tures in connection with both the pineal and parapineal organs.
Such observations have been made by Spencer ('86)36fi in Plica
nn/lira: by Duval and Kalt ('89)9'J in Anguisfragilis; by Carriere"
in 1SJH): by Prenant3" in 1893-94-96; by Leydig237 in 1890-91,
and by Francotte130 in 1896. Accessory organs were also found

,:•

•

A U

.

ig. OS The corneal scale in Calotcs. arconlin?; to Spencer, l.ssr.

in L<ic< rid riri/xir<i }yy Burckliardt "; in 1S94; by Francotte130 in
1896; by Klinckowstroem ('94)20'J in Iguana, and by Studnicka
('93)3vl in 1'xrnd.n/mx /Killns/. Accessory epiphysoal oi'ga.ns may
arix- citlici- IVoin I lie lateral wall of the end-vesicle of the pineal
organ or the under wall of the parietal eye. There are two
types of accessory organs: 1 ) accessory pineal organs, and 2)
accessory parietal eye organs. The following are the possibili-
tie> t'oi- accessory pineal organs:

THE PINEAL BODY 133

1. Evaginations of the distal end of the epiphysis as in Anguis
and Iguana.

2. Independent buds off the epiphysis or extrusions from
it held in relation by pigment strands of cells, as in Lacerta
vivipara.

3. Isolated extrusions from the end of the epiphysis.
Accessory parietal eye organs are less common. Carriere57

in 1890 showed a diverticulum from the under wall of the parietal
eye. Prenant312 in 1895 made the same observation. Fran-
cotte127 found that these accessories consist of a lens and retina
which are still in connection with the chief organ. Accessory
organs usually have pigment in them, but this is not so in Phry-
nosoma and Sphenodon. Only the under wall is pigmented as
a rule, so that the under wall corresponds to the retina while
the upper wall corresponds to the lens. Such accessory organs
attached to the parietal eye indicate an attempt to produce
another optic organ. Only exceptionally does the upper or
dorsal wall show a lens formation. In Pseudopus, Studnicka384
in 1893 found that the interior of the accessory parietal eye con-
tained a syncytium as does the actual parietal eye. Prenant312
in 1895 differentiated the following types of accessory organs in
Anguis:

1. Epiphyseal eye. This lies close to the epiphysis, yet sepa-
rated from it and is entirely derived from that organ.

2. Interparietal-epiphyseal eye. This is situated in the mid-
line between the epiphysis and the parietal eye. It is the most
frequent of the accessory parietal eye organs.

3. Intraparietal eye. This is connected with the retina and
under wall of the parietal eye or else is included in it.

4. Accessory chorioidal eye. This is found very infrequently.
It is widely separated from both parietal organs and presents
itself as a pigmented hollow vesicle lying on the upper surface
of the chorioid plexus.

Accessory parietal organ structures are most frequent in
embryos and tend to disappear in the adult. This observation
is agreed to by most authors.

134 i I;!;DI:I;I< K TILXKY AND LUTHER F. AVARRKN

])'\ih n nces observed in the </>//>h//x«il cn//i/>I<:c in ///<•

species of r<-/>i.il<* <ilr«i</// ///rc^i./i/aicd.
PROSAURIANS

1. S/>li< //<><l»/i imiicialiuH (Htttterift). Spencer ('86) ;367 Leydig
'91) ;23 Hoffmann ('90) ;187 Dendy C99)87 described a develop-
ment, as did also Schauinsland346 in 1899 and 1903.

The pineal organ in the embryo is a simple evaluation \vitli a
thin stalk which is solid. The walls of the end-vesicle have
]n;iiiy folds. Only the cells in the interior retain a brown pig-
ment. The parietal nerve, according to Spencer, is a prolonga-
tion from the end of the epiphysis. Such a connection does
exist in some adults, but is of a connective tissue character.
Dendy and Schauinsland identified the actual parietal nerve.
It arises in front of the epiphysis and is independent of it. The
parietal eye is conical or pyriform in shape and the retina and
lens are both well developed. In olden1 embryos the nerve
does not enter the middle, but rather comes into relation with
the posterior third of the eye. The structure of the retina
was most minutely described by Spencer, Leydig, and Dendy.
It has rod cells and several other layers of cells. It contains
pigment as well as a molecular layer and a layer of large gan-
glionic cells. The lens is bi-convex. The entire organ is sur-
rounded by a connective tissue capsule. Dendy mentions a
thin-walled sac in the embryo between the epiphysis and para-
physis. This undoubtedly is an accessory organ. $i)li>'ti<nlon
has a parietal foramen and a superficial apparatus usually con-
nected with the parietal eye.

SAIIMAXS — LACERTILIA VKKA.

< ii:< KOXIDAE. 1. Gecko verus. Spencer ('86). 3" In this spe-
cies only the epiphysis is present. Then1 is no parietal foramen
and no parietal spot.

2. /'luii/thirti/lii* muralis. Spencer ('86) ;3'17 Leydig ('91) ;238
Melrhers ( '99 ).--'''•'•' In this form there is no parietal eye, the
epiphysis being the only element to appear. This latter con-
sists of an end-vesicle which is large and thick-walled having
no folds; its stalk is short and solid. The entire pineal organ is

THE PINEAL BODY 135

flask-shaped. There are many intercellular spaces in the end-
vesicle. These same observations hold good for Mauritanicus.

3. Hemidactylus verruculatus. Leydig ('91). 238 This species
possesses no parietal eye. There is an end-vesicle which con-
tains a brown pigment. The vesicle is drawn out into a small
point.

4. Hemidactylus mabouia. Stemmler ('OO).374 In this form
the pineal organ only is present and the end- vesicle is an atten-
uated bud. The proximal portion of the stalk is solid. There
is no pigment and no fibers in connection with the organ.

5. Gehyra oceanica. Stemmler ('00). 374 The parietal eye is
not well developed. The pineal organ alone makes its appear-
ance and has a definite end-vesicle. The stalk has a lumen in
its proximal portion. The cells in the end- vesicle are ependymal
in type. There are no folds in the wall.

AGAMIDAE. 1. Draco volans. Spencer ('86) ;367 Studnicka
('93). 3S4 There is no parietal eye in this species. The pineal
organ is a broad, dorsoventrally compressed end-vesicle con-
taining no pigment.

2. Ceratophora aspera. Spencer ('86). 367 In this form there
is no parietal eye. An end-vesicle develops, but there is no
parietal foramen.

3. Lyriocephalus sculatus. Spencer ('86). 367 There is no
parietal eye in this species. An end-vesicle exists with an
attenuated stalk. There is no pigment, but the animal has a
definite parietal spot.

4. Calotes ophiomachiis and versicolor. Spencer ('86). 367 The
epiphysis ends at the edge of the parietal foramen. The
parietal eye is present. Spencer saw only rods in the retina.
The lens is concavo-convex. Some of the lens cells and retinal
cells are pigmented. A well-marked parietal foramen is present
and there is a small modified cornea with parietal spots.

5. Agama hispida. Spencer ('86). 367 This species has a
parietal eye, a retina, lens, and a parietal foramen, together
with a cornea and parietal spot.

6. Grammatophora barbata. Spencer ('86). 367 In this form
there was found some evidence of a parietal eye, the under

KKKDI.UCK TIl.XKY AM) LUTHER F. WARREN

wall of which was definitely pigmented. .McKay ('SS)2^ found
a l>i-c< >n vexed lens, a good retina witli rod cells and round cell-,
:i molecular layer, and also a spindle-celled layer and peculiar,
triangular element --. The lumen was traversed )>y a fine strand.

7. Mnlndi liom'ilii*. Spencer (/SO).367 In this species the
organ is strongly pigniented, more likely an end-vesicle with a
stalk than a parietal eye. The parietal foramen in which the
organ rests is present. Both cornea and parietal spot are
present.

8. Ai/d/tni cdncdx/cd. Owsiannikow ('88). 295 In this species
there is a relatively large parietal eye with rods in the retina,
which latter is otherwise well developed, There is also a lens,
a parietal foramen, a vitreous, cornea, and a parietal spot. In
one case, Ritter ('94) 333 found an accessory organ which he
called the parapineal organ. It was situated in the parietal
foramen somewhat to the left of the parietal eye. No corium
was above it. A common, connective tissue capsule contained
both organs. The accessory organ was larger than the parietal
eye. There was no lens or retina in the accessory organ.

(.). Phrynocephaliis VlangaliL Owsiannikow ('88). 295 In the
20 mm. embryo this species has a parietal eye. The organ is
deeply pigmented.

IGUANIDAE. 1. Phrynosoma orbiculan-. Stndnicka ('93). 384
In this species the epiphysis is broad and globular and con-
nected by a stalk to the roof of the brain. It presents an end-
bud on its distal extremity. Ependymal cells in the body con-
tain a brown pigment. In the lumen there is a coagulum which
consists of a syncytium of pigment-containing cells. The pari-
etal nerve was not observed. The parietal eye is small, dorso-
vcnt rally flattened with a well-developed lens and retina. The
lens is bi-convex. The cells of the lens have their nuclei situated
near the under surface. The retina is filled with pigment, hid-
ing its main structure. The position of the parietal eye is in a
wide foramen, four times as large as the parietal eye itself. The
parietal cornea and spot arc present.

2. . I//O//N. Spencer ('86) ,86? This species presents a well-devel-

oped parietal eye which is ovoid in form and has a well-developed,

THE PINEAL BODY 137

thick retina. The latter is pigmented and contains rod cells.
The lens is bi-convex. What Spencer considered a nerve was in
all probability connective-tissue remains of a former nerve. A
narrow parietal foramen occurs while the cornea and parietal
spot are absent.

3. Leiolcemus niiidus. Spencer ('86). 367 In this form the
epiphysis exists as a hollow, proximal part and a horizontal
solid end portion. The latter is stretched forward to reac the
parietal foramen. The parietal eye is dorsoventrally flattened
and has a narrow lumen. The upper surface of the retina is
flat and horizontal. The lens is present. There are rod cells
which are the chief elements in the retina. The lens is bi-
convex and the nuclei of the lens cells lie in a layer deeply
situated. There is a parietal foramen in which the eye is lodged.
The corium is clear. There is a light colored parietal spot.

4. Leiolaemus tennis. Spencer ('86). 367 The epiphysis ex-
tends forward to a well-marked parietal eye. There is no con-
nection between the two. The parietal eye has a pigmented
retina and a lens. The parietal cornea and parietal spot are
present.

5. Plica umbra. Spencer ('86). 367 The epiphysis has a prox-
imal part and a horizontal portion which is solid and reaches the
parietal eye. The latter is connected with the epiphyseal end-
sac. The parietal eye is much flattened and the retina is pig-
mented. It is situated in a deep parietal foramen. The cornea
is present as well as the parietal spot.

6. Iguana tuberculata. Spencer ('86) ;367 Leydig ('96) ;239
Klinckowstroem ('93). 207 In this form the epiphysis is well
developed with a large end-bud in connection with the proximal
portion. The latter has a more or less follicular appearance.
In embryos the cells have cilia, but these later disappear. Klinc-
kowstroem in the 18 mm. embryo describes a tractus pinealis in
the distal end of the epiphysis. A parietal nerve is described by
the same author in 1894. In embryonic stages it connects the
retina with the roof of the brain. The parietal eye is globular
and in some forms a highly differentiated retina is present. An
actual nerve layer appears only in the embryo and later disap-

FREDERICK TILXEY AND Ll'THER F. WAKKKX

pears. The pigment increases in the older animals. The lens
is plano-concave. The eye rests in a parietal foramen. The
cornea is present .'is well as a marked parietal spot.

7. ritrtinoxinnti tluiujlnsxi. Hitter ('91). 332 There is an epi-
physeal vesicle in this form and a posteriorly flattened vesicle
which contains no lumen. It is connected by a very thin stalk
to the epi])hy>is. The parietal eye is connected with the brain
roof and is a laterally compressed vesicle. The lens and retina
are In .th well developed. The retina has an outer cell layer, a
molrcul: r layer, and an inner layer with two elements, one round
and the other elongated, and finally an inner layer of rod cells.
There is a coagulum in the cavity of the eye vesicle. The lens
is slightly hi-convex. The nuclei of the lens cells lie near the
inner periphery of the lens. The position of the eye is in a
broad foramen. The parietal cornea and pit, as well as a pari-
ietal spot, are all present.

8. Ufa xHiHHlmriditd. Ritter ('91) ;332 Studnicka ('95). 386 The
parietal eye in this form is also ventrally flattciu d. The lens is
separated from the retina. There is deep pigment in the retina
and the eye rests in a parietal foramen.

9. SccirporHx // //</ ii la I us. Herrick ('91)17S in describing the
epiphysis in this form, states that the under wall -has some
similarity to the retina.

10. J'ln-i/naxotnd coronation. Ritter ('91) ;332 Sorensen ('93). 361
The epiphysis is similar to that in Phrynosoma doiiyla**!. It is a
thick-walled vesicle. The cells in the interior are deeply pig-
mented. There is a connective-tissue strand running to the
parietal eye. The parietal nerve extends from the conimissura
posterior to the parietal eye. The eye is not as well differ-
entiated as in Phrynosoma doiKjla^i, although it is present.

11. Xct It IHH-IIX .s7/'/V////x. Sorensen l'(.)4). In this form the
epiphysis is attached to the roof by a thin, peculiarly white
-talk. The parietal nerve presents no peculiarities, but arises
from the anterior portion of the comntissiira habenularis. It is
solid to the extreme end of the epiphysis where it proceeds to
the parietal eye, the latter apparently being independent of the
end of the epiphysis. \o parietal foramen is present. The

THE PINEAL BODY 139

parietal eye has the form of a dorsoventrally compressed sac
which has a lens and well-marked retina, the latter has a double
layer of well-pigment ed cells. Rod cells also are present. The
entire parietal organ is enclosed in a connective-tissue capsule.

ANGUIDAE. 1. Anguis fragilis. Leydig ('96) ;239 deGraaf
('86) ;155 Spencer (86) ;368 Beraneck ('92) ;23 Hanitsch ('88);169A
Strahl and Martin ('88) ;383 Francotte ('96) ;130 Owsiannikow
('88) ;295 Duval and Kalt ('89;)" Carriere ('90) ;57 Prenant,
('95), 312 and Studnicka ('93). 384

The epiphysis in this species consists of a proximal and a
distal portion. The end portion of the epiphysis is deeply
pigmented. The parietal eye is connected by a connective-
tissue strand to the epiphysis. . The parietal nerve is present
only in embryos and arises from the ganglion habenulae. The
parietal eye is lenticular in form, dorsoventrally flattened, and
has a deeply pigmented retina. The lens is bi-convex and plano-
convex. The lumen contains a coagulated substance with a
syncytium. There is a well-developed capsule. Accessory
organs are common. The position of the eye is in a parietal
foramen. The parietal cornea, pit, and spot are present.

2. Varanus bengalensis. Spencer ('86).36S The pineal organ
has a distal and proximal portion and there is no parietal nerve.
The parietal eye is present and contains a lumen. The retina
contains rod cells and several layers of smaller cells. The lens
is convexo-concave. The parietal foramen is of large size.
There is a capsule, a parietal pit, and a parietal spot.

3. Varanus nebulosus. Leydig ('91).23S In this species the
pineal organ is as in other forms, but there is no end-sac. The
parietal eye is pyriform but there is no distinct retina.

4. Pseudopus pallasi. Owsiannikow ('88) ;295 Hoffmann
('90), 187 in Bronns "Klassen and Ordnungen."

In this form there is a well-developed lens, retina, and vitreous.
Studnicka386 in 1895 described the conditions as follows: There
is a complete pineal organ with an end-vesicle, a stalk, and
proximal portion, the latter being the epiphysis. This is con-
nected with the brain-roof by a secondary stalk. The parietal
eye is semiglobuiar in shape. There is a. lens and retina, the

140 FREDERICK TII.NKV AM) U'THKl; F. WAKHKX

latter having r«»d celN. a layer of small celN and a layer of large,
probably ganglionic. cells. There is a parietal nerve and a con-
nective-tissue strand connect ing the organ to the e])iphysis.
The lens is bi-convex. An accessory organ is also present.
There is a capsule of connective-tissue and a broad parietal
foramen. A parietal cornea, pit. and spot also exist.

."). Varanits giganteus. Spencer (J86).868 In this form there is
no mention of an epiphysis. The parietal nerve has a special
feature. From the end of the epiphysis to the parietal eye such
a nerve is seen to extend. Two or three strands of the nerve
are found which become confluent. The parietal eye is dorso-
vent rally flattened. There is a lens and retina present, the
latter contains rod cells and several other layers. In the cavity
there is a vitreus. The lens is thin and bi-convex. In the
center is a mass of round cells deeply pigmented indicative of a
rudimentary character of the organ. The parietal capsule con-
sists of connective tissue. There is a parietal foramen, pit, and
spot.

6. Varan UK griseus. Edinger (00).10G This species shows, in
a sagittal section through the brain, an unusually large epi-
physis thrown into many folds. It resembles the epiphysis of
Pseudopw.

TEJIDAE. 1. Ameiva corvina. Spencer ('86). 366 In this form
neither a parietal foramen nor a corneal pit is present.

2. Tejus teguf.r/n. Klinckowstroem ('94). 209 An embryo of
this form seemed to show only a pineal organ well developed,
while above it was a rudimentary parietal eye. Studnicka884
does not believe the parietal eye develops in this form.

LACERTIDAE. 1. Lacerta vivipara. Spencer ('86) ;366 Owsian-
nikow f XX) ;-'•<•' Strahl and Martin ('88) ;383 Leydig ('91) ;238 Stud-
nicka ('93). 384 In this species the pineal organ is globular and
pyriform; its extremity alone contains pigment. This is con-
nected with the parietal eye by a vascular connective-tissue
strand. The parietal nerve is independent of this strand.
The parietal eye is a flattened vesicle and there is a much-re-
duced lumen. The retina is deeply pigmented; its structure is
obscured by this vesicle. The lens is In-convex. The capsule

THE PINEAL BODY 141-

is not well developed. The eye eventually makes its way into
the parietal foramen. The corneal pit is present.

2. Lacerta viridis. Spencer ('86) ;366 Leydig ('91). 238 In this
form, extending from the parietal organ into the epiphysis is
a fibrous strand. The end of the epiphysis is deeply pigmented.
The parietal eye is flattened dorsoventrally. The retinolen-
ticular transition is gradual. There is much pigment in the
retina. The lens is bi-convex. The parietal foramen is present.
There is a corneal pit, cornea, and a parietal spot.

3. Lacerta ocellata. Spencer ('86) ;366 Leydig ('91). 238 The
pineal organ is expended at its distal end with an end-sac proc-
ess. The wall is folded to form twelve accessory spaces in the
epiphysis. The end of the epiphysis is pigmented. There is a
parietal nerve and a well-developed parietal eye which is globu-
lar and slightly flattened. The retinolenticular transition is
gradual. The retina is pigmented and contains cylindrical and
ganglionic cells. The lens is bi-convex. The capsule is well
developed. The parietal foramen contains the eye. The
parietal cornea is present. There is also the parietal spot.

4. Lacerta agilis. Owsiannikow ('88) ;293 Leydig ('91) ;238
Studnicka ('93). 384 The pineal organ is present in the form of an
epiphysis, which is saccular and has a hollow stalk. The parietal
nerve, according to Leydig ('96), 239 is present. It takes origin in
the ganglion habenulae and extends to the parietal eye. This
eye is a flattened, saccular vesicle. The retina and lens are
sharply demarcated. The retina is less pigmented than in other
forms. It is connected with the brain by a parietal nerve. The
lens is bi-convex. There is a special parietal sheath made up of
connective tissue. The parietal foramen, corneal pit, and
parietal spot are present. Exceptionally, the foramen is closed
by bone.

5. Lacerta muralis. Leydig ('91) ;238 Studnicka ('93). 384
The epiphysis is present as is also the parietal eye. The retina
is deeply pigmented. The corneal pit and parietal spot are
also present.

SCINCIDAE. 1. Cyclodus cjigas. Spencer '86). 366 The pineal
organ arches forward over the hemispheres to enter the region

142 FREDERICK TILXKV AM) LITIIKH F. WARREN

of the parietal foramen. The epiphysis is hollow. The stalk
opens into the ventricle. The proximal tubular portion is
present. The di-tal portion is within the foramen. The end-
vesicle of the pineal organ comes into this relation. Spencer
thought it was a rudimentary eye. The corneal pit, parietal
foramen, and parietal spot are present.

'2. Chalddes trid<ict//hix. Spencer ('86) ;366 Leyclig ('91). 238
The epiphysis is a globular vesicle. The end is prolonged into a
tapering process. The epithelium is much thickened. The
parietal eye is separate from the epiphysis. The retinolenticular
transition is gradual. The lens is bi-convex. There is a parietal
foramen, cornea, spot, and pit.

3. Ilinnlin. McKay ('88) ;-'•••• Sorensen (J94).363 In this form
there is a well-developed parietal eye which is unattached to
the epiphysis. The lens is bi-convex. The retina contains
rod cells, round cells, a molecular layer, spindle cells, and pig-
ment cells.

4. ScinriiN tijUridnnlis. Prenant ('96). 313 There is a parietal
eye and a parietal foramen well developed in this form.

."). (iniKjijliiH oceHatus. Legge ('96). 228 In an embryonic
study of this form the epiphysis with a proximal portion and a
distal part was present. Only in the embryonic stages was the
parietal eye observed. It contains a brown pigment. There is
a lens which is bi-convex. The parietal nerve is not present.
The parietal cornea, foramen, and spot were not observed.

CHAMAELEOXTIDAE. 1. Chamaekon vulgaris. Spencer ('86)
Owsiannikow ('88) ;295 Studnicka ('93).;vl The pineal organ in
the form of the epiphysis is a folliculated. hollow sac, which is
flexed forward, the walls being much flattened. It runs out into
a long, strand-like point. The parietal nerve is probably not
present in the adult. The connection between the pineal organ
and the eye is connect ive t issue and not nerve. As to the pari-
etal eye, authors differ: some say there is a, good lens and retina,
others regard thi> as rudimentary in all respects. There is a
good capsule and a good parietal foramen. The parietal cornea,
pit , and spot are absent .

OFHIDIA. 1. /y/,,m rigris. IJabl-lliickhnrd ('94). In
this species there is an oval-shaped glandular struct lire, having

THE PINEAL BODY 143

many reduplications in its walls. It is rich in blood vessels
and has a small cell content. Over it lies the chorioid plexus.

2. Eutaenia sirtalis. Sorensen ('94). 363 The epiphysis in this
species is globular in form and glandular in structure. It is
embedded in connective tissue. Herrick ('91) 176 agrees in these
observations.

3. Tropidonotus natrix. Studnicka ('93) ;384 Leydig ('97).24°
In this form there is a paraphysis and epiphysis in older embryos
and in the adult. The epiphysis is definitely glandular in char-
acter. There is a thin stalk, the latter probably secondary
and not analogous to the stalk in lower forms. Ssobolew364 in
1907, working on embryos of Tropidonotus natrix and Vipera
berus, found that the epiphysis develops earlier than the para-
physis. The parietal eye does not appear in either of the forms
studied, nor is there a parietal foramen. The cells of the epi-
physis are arranged in colonies as in the glands of internal secre-
tion. The organ seems to have nothing to do with light per-
ception and the same applies to heat perception. There is no
parietal nerve and the primitive canal in the organ is lost (fig. 69) .

4. Tropidonotus rliombifer. Sorensen ('94) ,363 The epi-
physis is glandular in character.

5. Bascanium constrictor. Sorensen ('94). 363 In the embryo
of this species the epiphysis has a glandular form and is con-
nected with a stalk to the roof of the interbrain (fig. 70).

6. Coluber aesculapii. Studnicka ('93). 3S4 In this species
the epiphysis is globular in form and covered with connective
tissue. It contains a dark pigment and lies close to the brain.

7. Coronella austriaca. Leydig ('97).24° There is no parietal
organ in this species in relation with the skull. In the embryo
the epiphysis is well developed.

8. Pelias berus.- Hanitsch ('88);169A Studnicka ('93). 384 In
this species Hanitsch believed that he discerned a parietal organ
with much pigment and a lens. Studnicka disagrees with this
and describes the epiphysis as a typically glandular structure.

9. Vipera ursinii. Leydig ('97).24° In this species the struc-
ture is definitely glandular.

CHELONIA. 1. Chelone my das. Rabl-Ruckhard ('86). 322 In
this species the epiphysis is a massive, bilobed structure.

144

FREDERICK TIL.XKV AND U THFi; F. WAKKKX

2. Cixlinlu i urn/mi <i. Bojanus ('19). 36 This author first
de-cribed the epiphy>is in lliis form as a short, pediculated struc-
ure with a dilated extremity whicli was flexed forward. Faivre115
in 1S")7 describes it as a conical body containing small particles of
calcium phosphate. Ilerriek17'1 in 1891 defined it as a tabulated
sac attached to the roof of the brain. The distal portion is non-
vascular. Sorensen ('93), 361 reconstructed the pineal organ in
this form (fig. 71).

gj

.

CI'.I The epiphyseal complex in a youn.u; 'I'l-npidimotus natrix, :iccnrcling
to Lcydii: 1897.

3. Ax/)id»nc<-lrx */>/ n ifcr. Herrick ('91). 176 In this species
the epiphysis has the form of a tubular structure arching for-
ward. Its lumen opens into the ventricle through a short stalk.

4. ('l/i/i/ilrii wr/xi/l/nii. Humphrey ('94).19° The embryo
of this -pecies has the same form as the saurians. In the early
staue- it i< a dilated sac connected with the third ventricle by a
short -talk. Later this stalk becomes hollow and in adults it
shows lobulat ion.

THE PINEAL BODY

145

5. Amida muiica. Gage ('95).13!; The epiphysis in this
species is similar to other chelonians.

6. Chelone imbricata. Voeltzkow ('03).41° The epiphysis in
this species is entirely separated from the brain.

Fig. 70 The pineal region of Boscanium constrictor, according to Sorensen,
1894.

Pf., paraphysis; Ds.. dorsal sac; Ch., commissura habenularis; Ep., proxi-
mal portion of pineal organ; Sch., pars intercalaris posterior; cp., posterior
commissure.

Crocodilia. Sorensen ('94). 363 As already stated, this author
did not find the epiphysis or any portion of the parietal organ
in the alligator. Voeltzkow410 in 1903 in Crocodilus madagas-
cariensis found no epiphysis (fig. 72).

The conditions and relations of the epiphyseal complex
in Reptilia are so important as to necessitate the following
tabulation :

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THE PINEAL BODY

147

Ds.

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Fig. 71 The pineal body of Cistudo europaea. according to Sorensen, 1896.
Fig. 72 The pineal region in the Alligator, according to Sorensen, 1896.
Pf., paraphysis; Ds., dorsal sac; Ch., commissura habenularis; Cp., posterior
commissure; M., midbrain.

14X FREDERICK TILXEY AND LUTHER F. WARREX

The parietal or third eye does not make its appearance in
reptiles except in SjiJicmxInn and Lrurrliliti rent. In these
latter forms it is by no means constant. Of forty-four species
examined, the parietal eye has been observed in 29 instances,
the retina in 28, the lens in 24, the parietal nerve in 25, the
cornea in 24, and the parietal foramen in 28. It was impossible
to detect these structures in the same number of species as
follows: Parietal eye absent in 9, retina absent in 11, lens absent
in 10, nerve absent in 12, cornea absent in 10, and parietal fora-
men absent in 10. The pineal organ, either complete in all its
three portions or as the proximal portion (epiphysis proper),
was present in all of the forty-four species. A complete pineal
organ was observed in thirty-one species while a highly devel-
oped proximal portion, possibly suggestive of glandular forma-
tion, was present in eight species.

In Ophidia and Chelonia there was a total absence of the
parietal eye and structures pertaining thereto in all of the fifteen
species examined. In nine species of ophidians the pineal
organ was represented in nine instances by a definitely glandular
proximal portion, the epiphysis proper or corpus pineale. This
gland seems to contribute its secretion to the ventricles, but
may also be of the blood-vascular type as well. In Chelonia
there is evidence that the pineal organ which appears as the
proximal portion of that structure may also be glandular in
nature. The absence of the parietal eye elements as well as the
pineal organ has already been mentioned in Crocodilia.

It is evident from this summary that only the proximal por-
tion of the pineal organ persists in the more modern reptiles,
while the parapineal element as well as the end-vesicle and stalk
of the pineal organ, have entirely disappeared.

7. Comparative Anatomy and Hf.^tol <>(/// of the Epiphyseal Complex

in Birds

As in ophidians, the only element of the epiphyseal complex
which persists in birds is the proximal portion of the pineal
organ. This presents itself as the epiphysis or corpus pineale.

THE PINEAL BODY

149

In form the avian epiphysis is conical or cylindrical, sometimes
being flattened by the approximation of the cerebellum and
cerebral hemispheres. Its size varies considerably in different

lim

Fig. 73 The pineal region in Gallus domesticus, according to Studnicka, 1896.
Ds., dorsal sac; Ch., commissura habenularis; R., recessus pinealis; St., pineal
stalk; Ep.. pineal body; Cp., commissura posterior.

species, but the following figures give a general idea of the
dimensions.

In Meleagris gallopavo 5 mm. long by 2.5 mm. thick

In Gallus domesticus 2.5 mm. long by 1.5 mm. thick

In Strix 6 mm. long

150 FREDERICK TILNEY AND LUTHER F. WARREN

It is situated close to the roof of the interbrain, its long axis
being as a rule, perpendicular to the latter. In no instance does
it approach or come in contact with the inner surface of the
skull.

The histology of the structure discloses several different
forms which the organ may assume. Studnicka ('05), 391 distin-
guishes three distinct types: 1) A long sac with thick walls con-
taining many follicles. Such an organ is found in Passer — Gage
('95). 136 2) A solid body with communicating or independent
acini which connect with the lumen of the pineal body by means
of a still potent canal. Between the follicles are many blood
vessels and much connective tissue. The stalk is solid as in
Meleayris gallopavo — Mihalkovicz ('77). 275 3) A solid organ in
which there are solid, blind acini instead of hollow follicles.
These acini make up solid lobules.

In brief, these three types may be termed, 1) saccular; 2)
follicular or acinal, and, 3) solid. There are a number of
transitional forms in addition to those already mentioned.

Funkquist133 in 1912 describes two morphogenetic types in
birds.

1. The organ has a simple tubular character which, during
growth, shows a thickening of its walls and a general enlarge-
ment. In some cases the organ is solid except at its base where
it retains a cavity, the recessus pinealis.

2. In this type the organ has a tubular character, in many
instances retaining its connection with the original pineal evagi-
nation and in others being cut off from it. These bud-like
tubular processes resemble tubuli of the dorsal sac. The pineal
organ has its original anlage in an epithelial structure. Later,
development causes a transition into neuroglia tissue in much
the same way as the transition occurs in the central nervous
system. In some cases (canary and turkey) the acinus-for-
mation, giving rise to simple pineal tubules, persists, while in
other instances these acini are more or less obliterated.

Two types of cells may be identified, according to Funkquist,
namely, large epithelial cells with clear protoplasm and small
darkly staining cells.

THE PINEAL BODY

151

Fig. 74. The pineal body in Coccothraustes vulgaris, according to Studnicka,
1896.

152

FRKDKIJK K TILXEY AND LUTHER F. WAKHEX

( ialeotti11" in ISlMi also recognized two types of cells, i.e.r
radially/ arranged, cylindrical cells which hound the lumen of

\\

Fig. 75 The pim-:il luxly in Mclc.-i^ris n:illnp:iv<t. :ir<'<>nliii.u, t<> SI utlnirka, IS'.Ki.

the (»i-n;;!ii and small cells l>et\v<eii the larger ones. In the large,
cylindrical cells, (ijileolli tound hyaline masses which he con-
- dered a secretory produci ultimately delivered to the lumen of

THE PINEAL BODY

153

i,he acini. Studnicka391 regarded these cells as ependymal in
type just as in the lower vertebrates, but found no sensory cells.
In addition to the ependymal elements there were neuroglia
cells, and Studnicka in Meleagris also observed some very large
cells with clear cytoplasm scattered among the other groups.
There may be ganglionic cells, as in Acipenser. No nerve fibers
were observed. The epiphysis contains many isolated cells and
a secretion derived apparently from the ependymal cells. No
pigment was observed.

''^-^'^Kv.. ^JP^ritfJ

•'-"> • ' \^< \(;«T^^™_ ~v'l< IjCi-^l

-^.^s^a;-^s=%^=*^^5#«&»_ -® >^s^^-=^^S=^^Er*> ,t«^J'- » a ia r' /», w

_ ^:%-

Fig. 76 Section of the pineal body of Meleagris gallopavo, showing follicles,
according to Studnicka, 1896.

The stalk of the epiphysis, which is of course in no sense
homologous with the stalk of the pineal organ, being a secondary
character of the epiphysis, is usually short and contains the
recessus pinealis. In some instances, however, it is solid. No
nerve fibers have been observed in it, so that the organ has no
neural connection with the brain. The epiphysis, including its
stalk or peduncle, is enclosed within a sheath of pia mater and
arachnoid.

154 FREDERICK TILNEY AND LUTHER F. WARREN

Klinckowstroem206 in 1892 has shown in certain aquatic birds
during embryonic stages, a very early appearing, peculiarly
pigmented spot on the head. This he found in twelve out of
two hundred embryos of Sterna hirundo, Larus canus, Larus
marinus, Larus glaucus, and Anser brachyrhynchus. In adults
of these forms no such spot exists. There is little evidence to
indicate the tendency to the formation of a parietal foramen.

Dexter ('02) 90 observed in Gallus domesticus that the para-
physis is an appendix of the paraphyseal arch, developed from
the brain wall. He believes it to be glandular in character.
In the adult of this form it is composed of a modified ectodermic
tissue. In the younger stages its walls are thin and its cavity
is large, but in the adult chicken or hen the reverse is true. It is
oval in shape and lies nearly parallel with the longitudinal axis
of the cavity of the forebrain. It is a constant structure, and
Dexter has identified it time and again in the embryo, in the
chicken, and finally in the full-grown fowl. Its position is very
characteristic. The paraphysis is situated immediately dorsad
to the foramen of Munro and anterior to the prominent fold of
the chorioid plexus which must morphologically correspond to
the velum transversum.

Differences observed in the epiphyseal complex in the various
species of birds already investigated.

1. Gallus domesticm. Stieda ('69) ;376 Dexter ('02) ;90 Galeotti
('96).14° It was observed in this form that the epiphysis is
follicular in structure and glandular in character.

2. Meleagris c/allopavo. Mihalkovicz ('77)275 observed that
the epiphysis is follicular in this form.

3. Sterna hirundo. Klinckowstroem ('92) 206 found remains of
the parietal spot in the embryo.

4. Anas domesticata. Klinckowstroem ('92).20G In this form
the author observed that the epiphysis is follicular.

5. Apteryz. Parker ('92). 301 The epiphysis in this form is
usually anteflexed, although in some instances it is dorsiflexed.

6. Perdix cinerea. Studnicka (96).386 The epiphysis in this
species is follicular.

7. Strix flammea. Studnicka ('96).38fi In this form the epi-
pliysis is partly solid and partly follicular.

THE PINEAL BODY 155

8. Lanius excubitor. Studnicka ('96). 386 In this species the
epiphysis is saccular.

9. Turdus pilaris. Studnicka ('96). 386 The epiphysis is follic-
ular in this form.

10. Coccothraustes vulgaris. Studnicka ('96). 386 In this
species the epiphysis is hollow and saccular in its entire extent.

11. Passer domesiicus. Gage ('95). 136 The epiphysis is
hollow and saccular in this form.

In birds, as in ophidians, the evidence of the glandular nature
of the epiphysis is pronounced. Every form examined yields
many suggestive indications that the pineal body in birds is a
glandular organ. The element pertaining to the parietal eye
has not been observed in the avian forms examined and the
epiphysis is evidently the highly specialized proximal portion of
the pineal organ. The stalk and end-vesicle have disappeared.
The element referred to in birds as the stalk is something entirely
different from that portion of the lower forms which connects
the proximal portion and the end-vesicle. The avian stalk is a
secondary development consequent upon the marked enlarge-
ment and solidification of the proximal portion. During this
process the pineal body tends to move slightly away from the
roof, and in so doing produces an elongation in the originally
constricted area which connects the epiphysis with the roof of
the interbrain. This, in contradistinction to the stalk of the
end-vesicle, is the stalk or peduncle of the epiphysis. The pineal
recess contained within this peduncle is not entirely homologous
with the pineal recess of the lower forms, for in the latter in-
stances the recess extends into the proximal portion its entire
length, while in birds it is restricted to the peduncle.

8. Comparative anatomy and histology of the epiphyseal complex

in mammals

In mammals the only element of the epiphyseal complex
which persists is the proximal portion of the pineal organ. In
but a single instance thus far recorded is there evidence of the
parapineal element, i.e., Cutore's74 observation of a small anterior

156 KRKDKRICK TILXKV AM) LTTHKIi F. WARREN

protuberance in front of the epiphysis in the new-horn Bos
lain-iix. As ;i rule, the proximal portion is solid in the greater
part of its extent and at turned by a more or less constricted
portion to the roof of the interbrain. This part of the epiphysis,
sometimes referred to as the stalk, is not to be confused with the
stalk of the lower vertebrates which, together \vith the end-
vesicle, fails to develop in mammals. The mammalian stalk is
more properly designated the pineal peduncle. The solid por-
tion of the epiphysis is regarded by many as a glandular struc-
ture, and hence the term pineal gland. In mammals the follow-
ing parts may be defined: The epiphysis or pineal body which
consists of 1) the pineal gland and 2) the pineal peduncle. In
the latter there is a recess of greater or less extent, the pineal
recess. The peduncle consists in a large part of nerve fibers,
while the pineal gland comprises several different constituents.
In man the peduncle becomes so specialized in the nerve fibers
which enter it as to constitute, according to some authorities,
distinct peduncular bundles or epiphyseal peduncles.

The form of the pineal body in mammals varies considerably.
It is for the most part cone-shaped ; it may be long or relatively
short. In marsupials it is round or pyriform. In rodents it is,
according to Flesch,121 more or less cylindrical, or, as Cutore76
states, cylindricoconical. In the pig, d'Erchia109 describes it as
spindle-shaped. In carnivores and primates the organ is gen-
erally conical or oval. According to Schwalbe ('81 ),348 it is a
dorsoventrally flattened globule. In the primates the peduncle
is paired, with the exception of Troglodyte* ni(/cr, in which,
according to M oiler ('90), 279 the epiphysis is kidney-shaped and
connected with the brain by means of a single unpaired stalk
4 mm. in length. The epiphysis in most mammals is dorsiflexe<l
so that its free extremity is directed toward the cerebellum. It
thus presents a ventral surface in relation with the midbrain,
a dorsal surface usually in relation with the corpus rallosum
(although there are certain exceptions to this statement), a.
base related to the roof of the interbrain, and an apex. The
dorsal sin-fare is in contact with a reduplication of the dorsal
sac known as the lamina superior pedirulorum and also with

THE PINEAL BODY

157

the remnant of the pars intercalaris anterior forming the lamina
inferior. These two laminae form the walls of a cul-de-sac, the
suprapineal recess. The small space bounded by the pineal
peduncle is the pineal recess.

In regard to its relation to the corpus callosum, Cutore ('10)76
states that there are three varieties of the pineal body in mam-
mals, i.e., 1) subcallosal, as in marsupials, some artiodactyla,
insectivora, carnivora, and primates; 2) retrocallosal, as in
most artiodactyla and perissodactyla; 3) supracallosal, as in
rodents. Cutore ('10) 76 gives the following figures indicating
the relative weight of the pineal body to the brain and also
the pineal index:

ANIMAL

WEIGHT OF BRAIN

WEIGHT OP
EPIPHYSIS

PINEAL INDEX

Sheep

grams
480 00

grains

0 350

0 070

Pig..

140 00

0 040

0 020

Goat

119.80

0.075

0.060

Horse

512 00

0.440

0.080

Ass

420 00

0.520

0.100

Mule

430 00

0 860

0 200

Rabbit

8 46

0 010

0.100

Rat

1 86

0.002

0.100

Dog..

85 20

0.080

0.005

Man

1300 00

0.220

0.010

The following tables give the diameters of the pineal body in
man, according to several different observers, and also the
differences at different periods of development as reported by
Cutore:76

Diameter of the pineal body in man in millimeters

HENLE

SCHWALBE

LORD

TESTUT

ROMITI

CHARPY

CUTORE

Longitudinal

8

12

5-9

7-8

12

10-12

9-10

Transverse

6

8

3-8

4-6

8

5-8

5-7

Anteroposterior... .

4

2-4

4

5

4-5

158

FREDERICK TILNEY AND LUTHER F. WARREN

AGE

SEX

WEIGHT OF
BODY

LENGTH OF
BODY

ANTEROPO.STKK-
IOR DIAMETER
OF BHAIN

TRANSVERSE
DIAMETEH
OF BRAIN

WEIGHT OF
BRAIN

WEIGHT OF
HYPOPHYSIS

WEIGHT OF
PINEAL BODY

Xcvvhorn

Female

gra m •>•

2,322

cm.

49.5

cm.

10.0

cm.

8.6

grams

340

grams

0.032

gra m a

0.007

S davs

Female

3,030

50.0

11.5

8.8

395

0.100

0.010

1 month

Female

2,207

52.0

11.5

9.4

470

0.100

0.040

3 months . .

Male

3,700

63.0

13 8

11 4

762

0 110

0 035

6 months

Male

5,700

67.0

14 9

10.8

793

0 115

0 053

10 months

Female

5,972

73.0

15 0

12 0

836

0.160

0 045

13 months

Female

6,390

68.0

15 0

12 0

795

0.140

0 060

15 months

Male

6,550

73.0

17 0

12.5

872

0.170

0.025

15 months

Male

4,248

73.0

14 4

11.0

507

0.120

0.080

18 months

Female

6,200

73.5

15.8

12.5

905

0.160

0 050

20 months

Female

6,722

7-4.0

15.3

11.3

710

0.180

0.060

3 years, 3 months. . . .
3 years, 6 months. . . .
4 years

Male

Male
Female

5,625
8,208

80.0

84.0
91.0

16.1
15.9
16.5

12.0
12.9
11.8

990
1,000
1,075

0.192
0.200
0.190

0.093
0.050
0.070

9 years

Male

115.0

17.7

14.3

1,100

0.250

0.100

11 years

Male

120.0

17.2

13.5

1,257

0.400

0.120

13 years

Female

130.0

16.7

13.1

1,219

0.340

0.170

18 years

Male

142.0

16.7

13.2

1,200

0.310

0.125

19 years

Female

150.0

17.5

13.1

1,193

0.320

0.060

22 years

Female

165.0

18.0

13.3

1,237

0.690

0.070

23 years

Male

162.0

16.9

12.5

1,162

0.780

0.120

24 years

Male

163.0

17.9

13.6

1,300

0.440

0.220

60 years

Female

152.0

17.2

14.0

1,273

0.440

0.100

70 years

Female

147.0

16.9

13.0

1.000

0.650

0.140

70 years

Female

149.0

17.2

13.0

1,102

0.420

0.150

In the development of the pineal organ in all vertebrates,
only two of the germ layers play a part, i.e., the ectoderm and
the mesoderm. It is advantageous, therefore, in considering the
histological character of the pineal body, concerning which there
is much difference of opinion, to discuss the ectodermogenic
and mesodennogenic elements entering into that body. Of the
elements derived from the ectoderm the following have been
observed: 1) parenchymal cells, 2) ependymal cells, 3) neuroglial
cells, 4) ganglionie cells, and 5) nerve fibers. The following ele-
ments derived from the mesoderm have been described: 1) con-
nective tissue cells, 2) connective tissue Inibeculae, 3) blood

THE PINEAL BODY 159

vessels, 4) certain cells called muscle or myoid cells, 5) lympho-
cytes, and 6) lymphoid reticulum.

Hollard188 in 1837 regarded the epiphysis as a glandular struc-
ture with nerve fibers in its peduncle only. Valentin403 in 1843
believed that the pineal body possessed a parenchyma which
was something entirely different from the gray matter of the
brain. He observed certain 'nuclear formations' which had a
striking resemblance to the tissue of the pituitary gland. Kolli-
ker210 in 1850 described the epiphysis in mammals as consisting
of small, round cells, multipolar nerve cells and compact bundles
of nerve fibers. But it is to Faivre114 in 1855 that we are
indebted for the first extensive study in the comparative his-
tology of the epiphysis. Faivre investigated microscopically
the pineal body of man, horse, guinea-pig, dog, ox, rabbit, and
pig. He recognized three elements in the human pineal body,
i.e., 1) a fibro vascular envelope, 2) a globular parenchyma, and
3) acervulus cerebri. Faivre's observation was in accord with
Valentin's,403 that the pineal body differs essentially from the
brain. He concludes that the parenchyma is made up largely
of those globules which were nuclei of large elliptical cells in the
organ. He seems to have been the first to recognize that these
cells contained granules and also that the parenchymal cells
were smaller in the child than in the adult. Clarke69 in 1860
found nerve fibers, nuclei and brain sand, but no nerve cells.
These elements were arranged in a reticular structure which
resembled the olfactory mucous membrane. Luys253 in 1865
considered the organ as a structure composed of nerve cells
and fibers, in general, analogous to the mammillary bodies.
Leydig232 in 1868 states that the pineal body in the mouse
resembles the pituitary gland in reptiles with certain small
differences. Frey ('67) 131 observed in adults multipolar gan-
glionic cells, rounded cells without prolongations and isolated
nerve tubes. Meynert ('77) 271 asserts that the parallelism
between the pituitary body and the epiphysis is a mistaken
idea. The pineal body should be considered a ganglionic deriva-
tive of the tegmentum. It contains two types of cells, one
having a diameter of 15 micromillimeters, the others 6 micro-

160 FREDERICK TILXEV AXI) LUTHER F. WARREN

millimeters in diameter. It differs from other ganglia only in
the fact that the cells are much closer together. Krause ('68)219
described ner\ •<> libers in the epiphyisis having a double contour.
Stieda ('69)376 observed anastomosing processes of cytoplasm
with nuclei in a reticulum. Bizzozero (71)32 found two distinct
elements in the organ, namely, stroma consisting of prolongations
of the capsule and a definite parenchyma. In this latter were
two types of cells. In the larger of these the cytoplasm con-
tained granules. He noted that the pineal gland in the new-
born and in the infant contains the same elements as in the
adult. The only difference is in the fact that the smaller ele-
ments have a few branches while the larger cells have none.
The cells are arranged in alveoli. Meynert (77) 271 concluded
that the epiphysis was a nerve ganglion. Hagemann (72) 164
found two types of epithelial cells, namely, round cells and
fusiform cells which are bipolar and multipolar nerve cells.
The pineal body, in his opinion, is a combination of epithelial
cells and nerve cells. Cruveilhier (77) 73 found in the epiphysis
pale, round cells, small nerve cells, large multipolar cells, and
calcareous concretions. Mihalkovicz (77) 275 concluded that the
pineal cells were not lymphatic corpuscles, but resembled the
cells in the lining of the cerebral ventricles. Schwalbe ('81)34S
considered the pineal cells to be modified epithelium with a
striking resemblance to lymphatic corpuscles. Cionini ('85-
'86)66, 67 fjrst demonstrated the presence of neuroglial elements,
the nerve fibers observed belonging to the blood vessels. Dark-
srhewitsch ('86) 79 refutes the idea that the pineal body is nothing
more than a 'simple gland.' By the Weigert method he found
the nerve fibers from the following sources: 1) internal capsule,
2) striae medullares, 3) Meynert 's bundle, 4) optic tract, and
5) posterior commissure. Meynert271 and Pawlowsky806 have
already noted the connection between the posterior commissure
and the pineal body. Henle172B in 18S7 considered the pineal
body as a lymphatic ganglion. Its parenchyma consisted of
two types of cells, i.e., round cells resembling lymph corpuscles
and angular cells with many points.

THE PINEAL BODY

161

Ellenberger ('87)HO maintains that the pineal body in the
horse is very similar to a lymphatic gland. It is highly vascular;
in it are but a few nerve fibers and these are difficult to trace to
their origin. Flesch ('88) 123 studied the pineal body in the
horse, pig, dog, bat, and man. He was able to find brain sand
in man only. He does not believe that the organ is rudimentary,
but regards it as an epithelial structure. There are some nerve

•<. ^m$tf&&$xwz! 's-'^^-^^S^^^^^ss

Fig. 77 Follicles and parenchyma of pineal body in man, showing concretion
of brain sand, according to Henle, 1879.

fibers in it. Its relation to the size of the brain is not definite.
It has, in Flesch's opinion, a physiological action in mammals,
is very vascular, while its specific cells contain pigment granules.
It seems to be a secretory organ and may contain a heat-regulat-
ing centre.

Edinger ('97)m found the pineal body in the higher mammals
to be formed of neuroglia cells. True nerve elements are
absent. Chauveau ('85) 64 observed groups of polyhedral cells

MEMOIR NO. 9

FREDERICK TILNEY AND LUTHER F. WARREN

separated by connective-tissue trabeculae. He also mentions
calcareous deposits in domestic animals. IMingazzini ('89) 276
believes the pineal elements resemble lymphatic corpuscles.
Soury ('99)365 found a substance like adenoid tissue filling the
spaces of a fine network. Weigert ('95)419 describes the pineal
body, especially its ventral portion, as composed of a thick
layer of neuroglia fibers of such a specific nature that the like of
it is not found elsewhere in the central nervous system. The
cells are very numerous and traversed by many fibers. Cajal
('95) 53 found sympathetic fibers entering the pineal body with
the vessels. These fibers form a rich interstitial plexus. The
fibers surround but do not penetrate the cytoplasm of the
glandular cells. Galeotti ('96-'97)14° makes the claim that
the pineal body is a secretory organ and believes there is evi-
dence of this in many vertebrates besides mammals. The pineal
cells elaborate a pigment in addition to their secretory product.
He recognized nerve cells which are in relation with the superior
and posterior commissures, ependymal cells constituting the
middle portion of the body, in relation with the pineal recess,
and epithelial cells which constitute the epiphyseal tube in some
animals and the epiphysis in mammals. Lord ('99)249 described
the parenchyma of the human pineal body as formed of small
stellate cells resembling those of adenoid tissue together with
other paler cells of variable size. Nicolas ('00)283B found striated
muscle cells in the distal portion of the pineal body in the ox and
calf. Dimitrova ('01), 92 a pupil of Nicolas', studied the pineal
body in mammals, young and old, including man, ox, calf, sheep,
horse, dog, and cat. She maintains that Nicolas' observations
were confirmed by her studies and that striped muscle cells do
occur in the pineal body of the ox and calf. In her opinion,
the essential constituent of the epiphysis in mammals is neuroglia
and she concludes that in addition to the essential neuroglial
nature of the pineal body there exists in the ox, calf, sheep, and
dog certain cavities which resemble thyroid vesicles <»r the
anterior pituitary lobe. In young cats some cells which are
independent of the neuroglia seem to resemble the elements
docribed by Cajal"1 and Retziusi:" v as sympathetic' and may be

THE PINEAL BODY

163

Fig. 78 A striated muscle fiber from the pineal body of Bos taurus, according
to Dimitrova, 1901 .

164

FREDERICK TILNEY AND LUTHER F. WARREN

neuroglia cells in process of development. Favaro ('04)n8
gives the following conclusions of his studies by means of the
Weigert method upon many mammals, including artiodactyla,
perissodactyla, rodentia, insectivora, carnivora, and primates.
Fibers found in relation to the pineal body are :
1. Prepineal fibers:

a) Transverse commissural

b) Oblique commissural

Fig. 79 Cells and fibers in the pineal body of Bos taurus (Weigert's method),
according to Dimitrova, 1901.

2. Fibrae seu fasciculus prepinealis.

3. Pineal fibers:

a) Superior transverse commissural fibers
6) Superior oblique commissural fibers

c) Posterior transverse commissural fibers

d) Diagonal commissural fibers

e) Superior and posterior fibrac propriae

Anglade and Ducos ('08-09)5 found neuroglia constantly
present in the human pineal body but also alveoli-formed cells

THE PINEAL BODY 165

of a different character. Sarteschi ('10)345 found that, as com-
pared with the adult animals, the epiphysis in the young rabbit
and guinea-pig was distinctly more glandular and in this regard
similar to the organ in birds. In the course of growth certain
regressive changes occur. Neuroglia and glandular cells were
present in all of the forms which Sarteschi studied. Constantini
('10)n studied the pineal body of the ox, horse, and man. He
describes two types of epithelial cells, i.e., 1) acidophiles and
2) basophiles. He concludes that the pineal body in mammals is
an organ of internal secretion. Cutore ('10), 76 on the basis of a
study of many different mammals, concludes that there are the
following histological elements in the pineal body: 1) Epithelial
cells containing granules and delimiting the cavities of tubules
or acini. 2) Lymphatic elements very numerous in larger
mammals and massed about the epipthelial cells. 3) Connec-
tive tissue forming trabeculae producing an apparent trabecula-
tion of the parenchyma. This connective tissue contains elastic
fibers, blood vessels, lymph spaces, and pigment cells probably
belonging to the category of mast cells. Some of the latter
cells give evidence of a process of fragmentation. 4) Cal-
careous concretions of calcium carbonate and phosphate. These
latter are sometimes found as inclusions in the cytoplasm or in
the meshes of the connective tissue. Cutore believes it to be an
organ of such complex structure, constituted of neuroglia,
epithelium, lymphatic and connective tissues, so arranged as to
form acini and so highly vascular, that it cannot be considered
to be in a state of regression as is claimed by Moller,278 Charpy,62
Dejerine,85 and others. Indeed, the highly specialized and char-
acteristic structure of the pineal body is sufficient justification
to attribute to it an internal secretory function. Galasescu
and Urechia ('10)137 found in the vicinity of some of the blood
vessels round and oval cells with deeply staining nuclei situated
centrally in a cytoplasm which stains with acid stains, e.g.,
eosin and fuchsin. The cytoplasm is granular and well demar-
cated. These acidophiles resemble those seen in the para-
thyroids. The authors propose to term these cells the 'para-
vascular acidophiles.' They believe these elements play a defi-
nite part in the internal secretion of the pineal body.

106

FREDERICK TILNEY AND LUTHER F. WARREN

B

'\K. 80 Neuroglia cells in the human pineal l><><ly

" f'ioniiii, ISS'J; B, according to Dimil rov:i, I'.MH.

method). A, :ic-

THE PINEAL BODY

167

Krabbe ('II)217 studied one hundred human pineal bodies,
both male and female, from birth to seven years of age and from
fourteen years to ninety-two years. There was a gap in his
subjects between the ages of seven and fourteen years. He
found two types of cells in the epiphysis: 1) special pineal cells
and 2) neuroglia cells. He thinks the granules in the cells leave
the protoplasm, traverse the intercellular space to enter the
blood, lymph, or cerebrospinal fluid, Krabbe does not agree
with Dimitrova92 that the fundamental element of the pineal

a

Fig. 81 Cells with granular protoplasm in the pineal body of Bos taurus (Wei-
gert's method), according to Dimitrova, 1901.

body is neuroglia, for he considers her criteria in distinguishing
neuroglia insufficient. He himself never observed muscle fibers
in any of the forms which he has studied. Krabbe concludes
that the epiphysis in man shows certain signs of involution,
as, for example, concretions, hyperplasia of connective tissue,
neuroglial plaques with cysts, and the presence of cells in a state
of disintegration. The involution begins at seven years of
age, but even in the adult the pineal body shows signs of active
function. The secretory process is manifest in the following

168 FREDERICK TILNEY AND LUTHER F. WARREN

manner: 1) basophilic granules in the nuclei; 2) the latter evac-
uated into cytoplasm. This process goes on during the entire
life of the individual even into old age.

Biondi ('12)49 calls attention to the finding of Constant ini71
and Galeotti140 of acidophiles in the pineal body. Biondi made
a special study for mitochondria by the method of Regand.
He was able to demonstrate small granules which he thinks
must be regarded as mitochondria. This he cites as evidence
of the secretory nature of the epiphysis. He calls attention to
the fact, however, that Nageotte281 and Mawas263 have both
stated that neuroglia cells also contain mitochondria.

Jordan, ('II)197 following the histogenesis of the pineal body
of the sheep, studied six stages from 5 cm. to 21 cm., also of the
eight months' lamb, yearling, and old sheep. He found no
muscle fibers. Between birth and the first year the pineal body
increases fivefold in size. In the fetus there are blind alveoli
and the organ is definitely lobulated by ingrowths from the pia.
Parenchymal cells form these alveoli. Vascular follicles are
abundant. The parenchyma consists of a more or less dif-
ferentiated ependyma. After the first year there are signs of
local degeneration manifesting themselves as an increase in con-
nective tissue, neuroglia, brain sand, clumps of pigment granules,
and a decrease of parenchyma! cells. The entire pineal body
decreases in size after the first year. He concludes that there
is no cytologic evidence in favor of the secretory function of the
sheep's pineal body. He points out, however, that the general
structure of the epiphysis, including its lobulation, its connec-
tive tissue framework, its parenchymal follicles, blind alveoli,
perivascular lymph spaces, great vascularity, and presence of
cytoplasmic granules, is indicative of a glandular function of
internal secretion. He interprets the cysts which appear in the
pineal body and the melanic cytoplasmic granules as probably
having an ancestral significance. In Jordan's opinion, if the
pineal body subserves any important function at all, this is
true only of the first eight months of postnatal life.

Jordan198 in the same year, studying the pineal body in the
(possum, states that the organ in this species has two forms:

THE PINEAL BODY

169

Fig. 82 Transverse section of the pineal body in the rat, according to Ramon
y Cajal, 1904

a-b, sympathetic nerve fibers; c., interstitial nerve plexus; Bl., blood vessel;
Hm , hemisphere

170

FREDERICK TILXEY AND LUTHER F. WARREN

-•," JT

I IL; si! I listo](ijiic;il characters of the pineal body in the sheep, according t»
Jordan. Kill.

THE PINEAL BODY 171

1) long and tubular, as in birds and reptiles; 2) short and
cup-shaped, resembling particularly that of carnivora. The
epiphysis is composed of a syncytial network, in the meshes of
which are scattered more or less highly differentiated or modified
ependymat cells and delicate bundles of nerve fibers. In the
opossum it appears to be in a state of instability. Its long,
tubular form connects it phylogenetically with the birds and
reptiles, while its short, cup-shaped form affiliates it with the
carnivora. Regarding the function of the pineal body in the
opossum, Jordan believes that his observations show it to be
unimportant in the body metabolism of mammals. This does
not necessarily mean that there is no specific secretion from
the organ, but rather that it has no direct or indirect influence
upon vegetative functions.

Nerve fibers in the mammalian epiphysis have been observed
by Kolliker210 in 1850, who appears to be the first to demonstrate
these elements. Krause219 in 1868 recognized the fact that the
fibers have a double contour, and Darkschewitsch79 in 1886
showed that they were myelinated nerve fibers. Connections
have been demonstrated to exist between the pineal body by
means of these fibers with the following parts: 1) internal capsule;

2) striae medullares; 3) Meynert's bundle; 4) optic tract by
Darkschewitsch, ('86) 79 and 5) posterior commissure by Meynert
(77),271 Pawlowsky (74),305 Cionini ('88),68 Favaro, ('04)118
and Cutore ('10) ;76 6) commissura habenularis by Kolliker ('50)21°
Hagemann (72), 164 Favaro ('04)118 and Cutore ('10), 76 7) sym-
pathetic system, Henle (79), 172 Cionini ('86), « and Cajal
('04). M Ganglion or nerve cells in the epiphysis have been
described by Kolliker210 in 1850 and Hagemann164 in 1872.
Cajal53 in 1895 also found ganglion cells in the pineal body and
described two types. Dimitrova92 in 1901 was able to find
ganglionic cells in young cats only.

Pigment has been found in the epiphysis of mammals by
Flesch123 ('88). Galeotti ('96)14° observed pigment particles in
the cytoplasm and nuclei. Dimitrova ('01) 92 found a golden-
brown pigment in the parenchymal cells. Cutore ('10) 76 ob-
served pigment in the pineal cells. Brain sand has been described

172 FREDERICK TILNEY AND LUTHER F. WARREN

by many authors in a number of mammals. Haller (1768) lfi5
considered it pathological, but Soemmering's3™ classical study
upon the acervulus clearly demonstrated that these concretions
are normal in man. Malacarne (1795)258 found brain sand in
the epiphysis of the goat. Wenzel (1812)420 described it in man
as being of two varieties according to its color, i.e., yellow or
white. Hagemann ('72) 164 considered it a normal constituent
of the adult pineal body in man. He also observed it in the ox.
Krause ('76)21S found it in many adult mammals. Flesch123
describes brain sand in the epiphysis of the horse, sheep, pig,
and dog.

A parietal foramen has never been observed in mammals, but
the white spot which frequently appears in the frontal region of
the horse's head has been suggested as a vestigial indication of
this aperture in the skull seen in many of the lower vertebrates.

Differences observed in the epiphyseal complex in the various
species of mammals already investigated.

MARSUPIALS. 1. Macropus giganteus. Lotheissen ('94).25° In
this species some nerve fibers penetrate into the substance of
the pineal gland. These come from the fasciculus retroflexus
of Meynert.271 They were not observed in other mammals.

2. Halmaturus dorsal is. Condorelli-Francaviglia ('95). 70 In
this form, because of the rudimentary corpus callosum, the pineal
body extends dorsad between the hemispheres. Its length is
2 mm. and its thickness 1.5 mm.

3. Didelphys vinjiniana. Jordan ('11).19S In the opossum
the pineal body occurs in two forms, i.e., either as a long tubular
organ or as a short, cup-shaped structure. It is composed of
ependymal cells in a syncytial network.

ARTIODACTYLA. 1. Bos taunts. Faivre ('55) ;m Hagemann
('72);1M Chauveau ('85)64 Nicolas ('00);283B Dimitrova ('01) ;92
Favaro ('04) ;117 Constantini ('10);7lV Cutore ('09). 74 In this
species the pineal body is cylindrico conical. Its diameters are :

cm.

Longitudinal 1 . •">

Trims verse 0.7

Anteroposterior 0.7

THE PINEAL BODY 173

It consists of large parenchymal cells, neuroglia, and lym-
phatic elements. It is very vascular. Cutore could find no
muscle cells. Some observers have found brain sand in the
organ.

2. Sus scrofa domesticus. Faivre ('55), 114 Hagemann (72) ;164
Flesch ('87) ;121 Favaro ('04) ;118 Cutore ('10). 76 In this form the
pineal body is long and pointed toward its distal extremity.
Its diameters are:

cm.

Longitudinal 1.0

Transverse 0.5

Anteroposterior 0.4

Fibers connect it with the ganglion habenulae and the pos-
terior commissure. It contains no concretions and no pigment.
Histologically it resembles the pineal body of Bos taurus.

3. Capra hircus. Malacarne ('95) ;258 Hagemann (72) ;164
Staderini ('97) ;372 Cutore ('10). 76 In this species the pineal
body is relatively short and conical. Its diameters are:

CT/l.

Longitudinal 0 . 70

Transverse 0 . 55

Anteroposterior 0.45

Malacarne described brain sand in the organ. Cutore could
find neither concretions nor pigment. Fibers connect the base
of the epiphysis to the posterior commissure and habenular
region.

4. Camelus dromedarius. Parisini.300 In this form the author
described concretions.

5. Ovis aries. Flesch ("87) ;127 Dimitrova ('01) ;92 Favaro
('04) ;118 Jordan ('II).199 In the adult of this species Jordan
describes signs of degeneration, including hyperplasia, brain
sand, clumps of pigment granules, and a decrease of parenchymal
cells.

PERISSODACTYLA. 1. Equus caballus. Faivre ('55) ;114 Hage-
mann (72) ;164 Ellenberger ('87) ;110 Flesch ('88) ;123 Favaro ('04) ;118
Cutore ('10).76 In this species the pineal body is conical. Its
diameters are:

174 FREDERICK TILNEY AND LUTHER F. WARREN

cm.

Longit udinal 0.8

Transverse 0.0

Anteroposterior ()..">

Nerve fibers are found in the base of the epiphysis. Histo-
logically, the pineal body consists principally of a delicate con-
nective-tissue framework, in the meshes of which are found
lymphatic elements. Many pigment cells are also found having
a brownish color and occupying usually a peri vascular position.
Xeuroglia and ependymal cells are also present.

2. Equiix < 1,^1 >i us. Cut ore ('10).7fi In this species the pineal
body is larger than in the horse and its form is oval. Its diam-
eters are:

cm.

Longitudinal 1.5

Transverse 0.6

Anteroposterior O.G

Its histology is much the same as that of the horse. Peri-
vascular pigmented cells are present in large numbers.

3. Eqmis mulus. Cutore f 10).7f> The pineal body in this
species is relatively large. Its diameters are:

cm.

Longitudinal 1.5

Transverse 0.6

Anteroposterior 0.6

It is conical in form. Histologically, it consists of paren-
chymal cells containing pigment granules. In addition, there
are ependymal cells, neuroglia, and lymphatic elements.

4. Elephas indicus. Parisini.300 In this animal Parisini
reports the presence of concretions.

INSECTIVORA. 1. Erinaceus europaeus. Cutore ('10).76 In
this species the epiphysis is triangular and is situated in the
intercollicular sulcus. It presents a well developed pineal recess.
Histologically, its elements resemble those of other mammals,
the cells being arranged in acini, not unlike the cellular forma-
tions in the hypophysis.

HODKNTIA. 1. Talpa. (ianser ('82). »2 In this form the
|)inc:il body was considered an unpaired ganglion habcnulae.
It receives fibers from the tlialanii and the posterior commissure.

THE PINEAL BODY 175

2. Lepus cuniculus. Tiedemann ('23) ;395 Marshall CGI);261
Krause ('68) ;219 Bizzozero ('68) ;30 Hagemann (72) ;lfi4 Mihalko-
vicz (77) ;275 Edinger ('97) ;104 Staderini ('97) ;372 Neumayer
('99) ;282 Favaro ('04) ;118 Cutore ('10) ;76 Sarteschi ('10).345

The pineal body in this species is long and cylindrical and of
such a shape as to justify the ancient term, penis cerebri. Its
diameters are :

cm.

Longitudinal 1.0

Transverse 0.3

Anteroposterior 0.2

Its histological appearance resembles that of adenoid tissue.
There are no pigment cells and no concretions.

3. Cavia cobaya. Faivre ('55) ;114 Hagemann (72) ;164 d'Erchia
('96);loy Staderini ('97) ;372 Favaro ('04) ;118 Cutore ('10) ;76 Sar-
teschi ('10).345 In this species the pineal body is similar in form
to that of the rabbit. Its diameters are:

cm.

Longitudinal 0.8

Transverse 0.4

Anteroposterior 0.3

Histologically, the organ resembles that of the rabbit.
4 Miis decumanus. Staderini '97 ;372 Cutore ('10). 7S The
pineal body in this species is elongated. Its diameters are:

cm.

Longitudinal 0.5

Transverse 0.3

Histologically, it presents a rich vascularization and paren-
chymal cells similar to those of other rodents. Pigment and
calcareous concretions are absent. Neuroglia, nerve fibers,
elastic fibers, and lymphatic elements are also observed.

5. Dasyprocta agouti. Sperino and Balli (;09).370 In this
species the form of the pineal body is cylindricoconical. Its
appearance is brownish, its apex is retroflexed so that the struc-
ture rests in the intercollicular sulcus. Its diameters are :

cm.

Longitudinal 0.5

Transverse . . .0.3

176 FREDERICK TILNEY AND LUTHER F. WARREN

CARNIVORA. 1. Phoca vitttlina and Rosmarus obesits. Tur-
ner ('88).40° In tho walrus and seal the pineal body has a greater
relative magnitude than in other mammals.

2. Cams futnilfaris. Tiedemann ('23) ;395 Faivre ('55) ;114
Flesch ('88) ;123 Dimitrova ('01) ;92 Favaro ('04) ;118 Cut-ore; ('10). 76
In this species the pineal body is conical in form. It is relatively
small. Its diameters are:

cm.

Longitudinal 0.4

Transverse 0.3

Anteroposterior 0.1

Histologically, it consists of neuroglia, nerve fibers, and
parenchymal cells which are polyhedral in form and arranged
in acini. Some cells contain pigment granules. In addition to
these elements there are large cylindrical ependymal cells.
There are no concretions present.

3. Felis domestica. Tilney ('15).396 The pineal body in
the cat is even smaller than in the dog and it is ovoid in form.
Its diameters are:

cm.

Longitudinal 0. 20

Transverse 0.15

Anteroposterior 0. 10

Histologically, it resembles the epiphysis of the dog.

4. Felis leo. Parisini.300 This author described concretions
in the pineal body of the lion.

PRIMATES. 1. Troglodytes niger. Moller ('90) ;278 Marshall
('61) ;261 Dendy and Nicolls ('II).88 In this species the pineal
gland lies in a groove between the superior colliculi and has an
unpaired peduncle. There is a deep pineal recess and a well
developed suprapineal recess. No concretions were described
in this species.

2. Macacus sinicus. Cutore ('12). 76 In this species the di-
mensions of the pineal body are:

cm.

Longitudinal 0.5

Transverse 0.2

Anteroposterior 0.2

THE PINEAL BODY 177

The pineal body is cylindricoconical in form in Macacus sinicus
and presents a great number of nerve fibers.

3. Cercopithecus griseus viridis. Cutore ('10). 76 In this
species the dimensions of the pineal body are:

cm.

Longitudinal 0.3

Transverse 0.2

Anteroposterior ' 0.2

The pineal body in this form is conical in shape. The struc-
ture of the organ is evidently glandular.

4. Homo sapiens. A large number of observers have given
their attention to the pineal body in man and many diverse
opinions have been expressed concerning it. Cutore's76 sum-
mary giving the histology and dimensions of the pineal body in
man is the most recent and complete review. The figures have
already been cited (p. 157). Cutore concludes that the human
pineal body develops slowly, retaining even up to the time of
birth its primitive diverticular form. In the adult, however,
this organ has become relatively voluminous and the original
recess is much reduced to form the ventriculus or recessus
pinealis. The superior or habenular commissure is small. The
pineal fibers are limited in number and distributed to the inferior
third of the organ. In the disposition of the parenchyma there
is seen a distinct tendency for the cells to arrange themselves
in circular areas clearly delimiting small cavities in which there
appears an amorphous or crystalline substance. Elastic tissue
is scanty, but pigment cells are numerous and concretions of
varying sizes appear in large numbers. The vascularization is
rich especially around the aciniform groups of cells. Neuroglia
and cylindrical ependymal cells are also present. Connective-
tissue processes from the pia mater form an irregular partition
of the tissue into lobules. Siegneur351 considers the pineal body
in man a gland, the cells of which are of two types, those which
are polyhedral with granules in the cytoplasm. These granules
are most numerous about the nucleus. Some of the cells have
vacuoles. The second type of cells are even larger and contain
large nuclei which stain deeply and occupy an excentric position in

MEMOIR NO. 9

178 FREDERICK TILNEY AND LUTHER F. WARREN

the protoplasm. In the new-born, lobation of the gland is much
more easily discerned than in the later periods of life.

The histology of the pineal body of the following mammals
has not heretofore been given, and as it seems to furnish some
details in the finer structure of the organ, the authors have
considered it advantageous to include these original observations
in this work. All of the material was obtained from the study
collections of the Department of Anatomy, Columbia University.
It includes specimens of Marcopits grayi, Camelus dromedarius,
<'<i />/•<! hylocrius, Zalophus calif or nianus, Lepus cuniculus, and
Simia satyrus. In addition to these species, the later stages of
development in the human fetus and in Felis domestica were
studied. The staining methods used were the Van Giesen,
haematoxylin-eosin, and Weigert's iron haematoxylin. On ac-
count of the limited amount of tissue it was impossible to do
any silver impregnation so that no evidence was obtained con-
cerning the nature of the nerve fibers in the pineal body.

1. Macropus grayi. In this species the cellular constituents
of the pineal body present the most striking features of any
of the mammals studied. Four types of cells are noted:

First. Large cells with extensive cytoplasm and a large vesicu-
lar nucleus. The nuclei of these cells stain very deeply.

Second. Cells of a similar size with vesicular nuclei which
stain feebly.

Third. Smaller cells with a large nucleus and a very small
amount of cytoplasm. The nuclei are intensely basophilic.

Fourth. Small cells with feebly staining nuclei showing many
granules.

The cells of these four varieties arrange themselves in a more
or less distinctive manner. The large epithelial elements of
both types nre disposed in such a way as to form well-defined
acini. Interspersed between these acinous groups are more or
less irregularly convoluted chains or cords of cells made up of
both varieties of the large type. The smaller cellular elements
are scattered among the cords and acini in an irregular manner.
Trabeculae of connective tissue serve to give the impression of
lobiilntioii to the structure, although thcs- lines of separation

THE PINEAL BODY 179

are irregular. The pineal body of Macropus is highly vascular.
The larger vessels follow the lines of the connective-tissue sep-
tum. No concretions were observed in any part of the pineal
body. The impression given by the arrangement and char-
acter of the cells in the pineal body of this species is that of a
glandular structure resembling in a general way this organ in
reptiles and birds (fig. 84).

2. Capra hylocrius. In this animal four types of cells may be
distinguished, as in the kangaroo. Here, however, the large
elements with a deeply staining nuclei are more abdundant and
a smaller number of the small cells with pycnotic nuclei are
observed. The arrangement of the cells is typically aciniform,
although there are areas in which no such disposition of the
cells can be made out. These portions of the pineal body,
therefore, in which the acini do appear stand out conspicuously
in contrast to the areas of the tissue in which the cellular arrange-
ment is more diffuse. The size of the acini varies greatly from
about 10 micra to 60 or 70 micra in diameter. The connective
tissue observed in the pineal body of the ibex is prominent both
because of the extensive network which it forms and also on
account of the unusual thickness of its trabecular strands. The
body is highly vascular and supplied by a rich capillary network
(fig. 85).

3. Camelus dromedarius. In the camel, as in Capra hylocrius,
four types of cells may be differentiated, namely, the large cells
with deeply staining nuclei, large cells with faintly staining
nuclei in which nucleolus and accessory nucleoli are distin-
guishable, small cells with deeply staining, and small cells of
faintly staining nuclei. The cellular arrangement has the same
general appearance as in the ibex, although the tendency toward
the formation of acini is not as pronounced. In the main, the
arrangment is that of wide strands of cells bounded by irregu-
larly disposed trabeculae of connective tissue. The connective
tissue forms a prominent element in the pineal body of the camel
and in general resembles the connective tissue of the Persian
ibex. The pineal body in the camel is highly vascular. There
were no concretions observed in it (fig. 86).

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THE PINEAL BODY 183

4. Zaiophus calif ornianus. In the sea-lion, although it is
difficult to discern the four types of cells already described with
clearness, as in the forms already noted, nevertheless, in certain
areas there appear many large cells with extensive nuclei which
stain deeply. Here and there scattered throughout the body
appear large cells of relatively the same size as those just men-
tioned, the nuclei of which, however, stain but faintly. Small
cells with deeply staining pycnotic nuclei are present in numbers
about equal to that of the first type while a small variety of
cell whose nucleus stains feebly is the least common variety
observed. The cells arrange themselves in cords or columns
which, upon transverse section, seem to be circular. These
cords apparently are much convoluted and not infrequently a
section of what appears to be the same cords is seen in transverse
as well as longitudinal outline. There is a rich connective tissue
network which appears to surround the cell cords. The pineal
body in Zaiophus is highly vascular. No concretions were
observed (fig. 87).

5. Lepus cuniculus. In the rabbit the pineal body is long and
cylindrical in form. In it may be recognized the four types of
cells already described, the predominant type being the large
cell with abundant granular cytoplasm and a large deeply stain-
ing nucleus. Dispersed among these cells are small cells of both
types and the large cells with faintly staining nuclei. The
general arrangement of the cells in this body is that of columns
or cords whose long axes are transverse to the axis of the pineal
gland itself. The columns of cells are separated by delicate
trabeculae of connective tissue in the meshes of which capillary
vessels make their way. Each of the cell cords varies in thick-
ness in different parts. They are seldom more than six to
eight cells deep, but in some places their transverse diameter
seems to be the thickness of two cells. The gland is very vas-
cular and no concretions are seen (fig. 88).

6. Simla satyrus. In the orang, it is not difficult to recognize
the four types of cells already described in the other forms.
Perhaps the chief difference in the histology of the gland in
this animal is the great prominence which the large cells attain

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186 FREDERICK TILXEY AND LUTHER F. WARREN

both because of their tendency to be collected into well-defined
groups, as well as the unusual dimensions of their cytoplasm.
Here, as in none of the other forms already described, does the
character of the pineal cell stand out. Not only is it much
larger, but it has the granular appearance so notable in the
human pineal cell. The large cells with the faintly staining
nuclei are found scattered among the cells just mentioned and
also scattered diffusely throughout the organ. The small cells
are less prominent, although both types may be recognized.
The cells are arranged according to an apparent design, although
the large pineal cells group themselves in irregular masses.
No tendency to cord formation is, however, observed. There
is a rich and delicate network of connective tissue, and many
capillaries surround the cell masses. No concretions were
ol) served (fig. 89).

7. Homo sapiens. In the adult human pineal body the types
of cells already described as present in the epiphysis of other
mammals may be observed here also. The large cells with
granular cytoplasm and large deeply staining nuclei are the
most prominent elements. They are arranged in regular masses
very similar to those observed in Simia salyrus, although the
intervening areas are less extensive, so that in man the cell
masses seem to run into each other without sharp line of demar-
cation. A very dense network of connective-tissue trabeculae
forms the frame work of the organ, while the vascularity of the
structure is richer than that of any other form observed. Con-
cretions of varying sizes are present throughout the entire
gland (fig. 90).

The histogenesis of the pineal gland was studied in the cat
and human. The inception of differentiation in the cat presents
itself as a marked thickening in the walls of the more caudal of
the two e vaginal ions. In the 70 mm. cat, this thickening is so
pronounced that the recess in the anlage is reduced to a narrow
lumen. The cells multiply at the caudal extremity of the no\v
;ilmost solid epiphysis. From the stage of 120 mm. to term a
process of diverticular formation occurs. This starts at the
base of the gland at its attachment to the roof-plate and grad-

THE PINEAL BODY

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ually extends to its distal extremity. Many of these diver-
ticula remain in connection with the third ventricle, but as they
elongate toward the tip of the pineal body many of the diver-
ticula lose this connection and finally appear as blind acini or
cell cords. In this way the original more or less indifferent cell
area of the primitive anlage is invaded by cells from the diver-
ticula above described. Simultaneous with the invasion of
these diverticula, blood vessels are seen to make their way into
the tissue between the acini and cell cords. This vascular
invasion seems to take place from the periphery going to the
center, but it is possible that independent blood spaces are
formed which, by concresence, subsequently form a vascular
network, the latter coming into relation with the blood vessels
surrounding the pineal body. These characters of the onto-
genesis of the pineal body in the cat are shown in figure 91.

The process just described in the histogenesis of the cat is
much better illustrated in the development of the human fetus.
In man, the process of diverticular invasion into the original
cellular mass of the primitive anlage is well shown in figure 92,
representing the condition in a human fetus of six months. Here
it will be noted that the invasion begins at the base of the epi-
physis and manifests itself in the thick strand of darkly staining
cells extending out and into a mass of undifferentiated tissue.
At term the invasion has extended completely through the epi-
physis and the deeply staining strands of cells are now arranged
in convoluted cords or take the form of apparent acini. In the
meshes between these cords capillaries appear to have made
their way in from the surface of the epiphysis and form a rich
network about the cell cords and apparent acini. This onto-
genetic differentiation in the two forms just described would
certainly seem to indicate a process which had as its object the
rich vascularization of discretely outlined epithelial areas. Such
a differentiation would seem to adapt itself best to the purposes
of internal secretion.

Marburg259 shows in the development of the pinoal gland in
man histological appearances very closely resembling those
illustrated in figures 91, 92, 93, and 94 of the authors (fig. 95).

190

1 KKDKKICK TILXF.Y AM) LUTHER F. WAKKKN

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THE PINEAL BODY

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Fig. 92 Section of the pineal body in a six months human fetus showing the
diverticular invasion, according to Tilney and Warren, 1917.

192

FREDERICK TILXEY AND LUTHER F. WARREN

THE PINEAL BODY

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194

FREDERICK TILXEY AND LUTHER F. WARREN

Marburg also gives an interesting description of the develop-
ment of the suprapineal recess in man which is illustrated in
figure 96. According to his description, the suprapineal recess
is formed by the dorsal reflection of the taenia which originally
was directed cephalad. The dorsal surface of the taenia secon-
darily becomes fused with the dorsal surface of the pineal gland
while the ventral surface is turned dorsad. In this way the
suprapineal recess results from a deep evagination of the roof-

Fig. 95 Cross section of the pineal gland in a 26 nun. human embryo, according
to Marburg, 1909.

plate which comes to lie above the pineal body and extends in
most cases the entire length of that organ. The suprapineal
recess in its relation to the pineal gland in adult man is shown in
figure 97.

With reference to the pineal body Mai-burg maintains that in
spite of all the involution processes in the gland, it cannot be
denied that even up to the late periods of life in man there arc
wholly intact glandular cells present in the organ which must
be taken to indicate a still existing function.

,-

97

Fig. 96 Scheme showing the development of the supra-pineal recess, according
to Marburg, 1909.

Fig. 97 The pineal gland in man, according to Marburg, 1909.

Ch., commissura habenularis; Cp., commissura posterior; Pl.ch., chorioid
plexus; Rp., recessus pinealis; Rs, recessus suprapinealis; Sch., pars intercalaris;
Th , taenia habenulae; Z, pineal gland.

195

196 FREDERICK TILNEY AND LUTHER F. WARREN

7. DISCUSSION

/. Significance of the pineal region

It is now possible, with the facts presented as evidence, to
discuss the problem of the pineal body and, perhaps, to formu-
late some conclusions concerning it.

The question uppermost about the epiphysis to-day is whether
the structure is a mere vestige or whether it has, in mammals
and more especially in man, some definite function. Besides
this highly important consideration there is still another which,
in its way, has an even more far-reaching significance, namely,
the value of the pineal structures as one of the indices which may
point out the lines of evolution running through the vertebrate
phylum and those leading back to the invertebrate, ancestral
stock.

If the pineal body is a vestige, it is essential to ascertain to
what previously active structures it is related and for what
reasons it has become vestigial. In this sense the survey of it s
phylogenetic relations cannot be too broad and should include
the entire environment of the organ. If, as is held by many, the
pineal organs have significance as a connecting link between
the vertebrates and invertebrates, then, on the basis of embry-
ology and comparative morphology, the effort must be made to
hornologize not one, but all of the parts associated with or
adjacent to the pineal body. In such a light every derivative
of the roof-plate of the primitive forebrain becomes funda-
mentally important, and no discussion of the pineal body could
be complete which did not recognize the character of the pineal
region as a whole.

The portion of the brain known as the pineal region was first
so designated by Minot277 in 1901. It has also been termed the
parietal region. It extends from the dorsal extremity of the
lamina terminalis to the caudal limit of the posterior commissure
and comprises all of the structures which develop from the roof-
plate of the primitive forebrain. It presents, according to
Minot,277 a scries of three arches or vaults, arranged one in
front of the other. The most cephalic of the three arches is

THE PINEAL BODY 197

the paraphyseal arch, which extends from the dorsal extremity
of the lamina terminalis to the most cephalic depression in the
roof, namely, the velum transversum. The portion of the roof
immediately caudad of the velum forms the middle or postvelar
arch, which in turn is separated from the third or caudalmost
arch by a slight depression containing the superior or habenular
commissure. This is the epiphyseal arch. In some species a
small intercalated portion of modified gray matter inserts itself
between the caudal limit of the postvelar arch and the superior
commissure. This is the pars intercalaris anterior. Caudally,
the epiphyseal arch extends toward the cephalic extremity of
the posterior commissure, but between the latter and the caudal
extremity of the arch there is interposed a small area of modified
gray matter, the pars intercalaris posterior. The caudalmost
element in the pineal region is the posterior commissure, and to
this, perhaps, should be added the subcommissural organ, recently
described by Dendy and Nicolls88 and others.

These structures of the pineal region or their homologues exist
in all vertebrates either in the embryonic or adult condition.
The paraphyseal or prevelar arch is common to all vertebrates.
From its caudal portion, i.e., the region of the arch nearest the
velum transversum, there develops a specialized structure, the
paraphysis. This structure, either in anlage or as an adult
organ, appears in all vertebrates.

In cyclostomes (Kupffer224 in Ammoccetes, Burckhardt47 in
Petromyzon) the paraphysis is a small sac-like diverticulum, if
not itself highly vascular yet in close relation with the vascular
mesenchyme immediately above it. In selachians (Minot277
and Locy243 in Acanthias) the structure is a small outgrowth
from the paraphyseal arch. In ganoids (Kupffer223 in Acipenser,
Hill,180 Eycleshymer and Davis113 in Amid) the paraphysis is a
large diverticulated and vascular organ. In many teleosts
(Burckhardt,47 Studnicka,391 and Terry)392 the paraphysis appears
to be rudimentary. In dipnoians (Burckhardt44 in Protopterus)
the organ is a wide outgrowth with many small diverticula and
rich in blood vessels. The paraphysis in amphibians attains its
greatest conspicuity as an organ. It is highly differentiated in

IDS FREDERICK TILNKY AND LVTHER F. WARREN

the adult (Warren416 in Xecturiis, Osborn289 in Siredon, Siren
and Proteus.) It is an elaborately folded, glandular structure
(Burckhardt 4S in Triton- and Ichihyophis), a solid vascular
mass (Sorensen361 in Menopoma), or a tubular and digitated
structure (Eycleshymer112 in Amblystoma) . In Rana, accord-
ing to Minot,-77 the paraphysis is characterized by a glandular
epithelium, a tubular arrangement of its cells, and an appar-
ently sinusoidal circulation, In Lacertilia (Warren415 in Lacerta
mural is, L. agilis and L. viridis) it is large and glandular in
character, forming a conspicuous element of the pineal region.
In many instances it is so extensive as to reach caudad as far
as the midbrain, or even the cerebellum. In ophidians, chelo-
nians and crocodilians, the paraphysis is small and rudimentary.
In birds it was first demonstrated in the chick by Selenka352 and
later described by Minot277 in the chick and Burckhardt4" in
the embryo crow. Dexter90 found it constant in the chick and
common fowl. He believes it to be a gland in which there are
no sensory elements.

In mammals Selenka352 gave the first description of the para-
physis in the opossum. Francotte128 observed it in a 12 mm.
human embryo. Usually, however, although it has been recog-
nized in anlage, in mammals it disappears early and the para-
physeal arch bears no trace of it in the fetal period.

Thus it will be seen that the glandular nature of the para-
physis in the middle portion of the phyletic series, including
amphibia and lacertilia, is quite beyond dispute. Some of this
character it retains in the more modern reptiles and birds. On
the other hand, it is relatively inconspicuous as an organ among
the lowest vertebrates and disappears altogether is most mam-
mals. Manifestly, therefore, whatever tendency toward speciali-
zation the paraphysis presents is in the interest of glandular
formation. As a gland, it appears either to contribute its secre-
tion directly to the cerebrospinal fluid in the ventricles or in-
directly to the blood. In no instance is there evidence of a
tendency toward the development of senson structure nor do
the histologie.'il elements entering into the paraphysis suggest
its direct participation in any neural mechanism.

THE PINEAL BODY 199

From the remainder of the paraphyseal arch there develop
in many classes of vertebrates several chorioidal processes. In
cyclostomes, selachians, teleosts, and ganoids, two such plexuses,
more or less well developed, may be recognized, namely, the
lateral and inferior telencephalic chorioid plexuses. The inferior
chorioid plexus attains its most marked proportions in amphibia,
while in all of the higher vertebrates its prominence declines.
This is likewise true of the lateral chorioid plexus. Histologi-
cally and topographically, the significance of these plexuses is
not difficult to discern; their rich vascularization, their tendency
toward glomerular arrangement together with the relations and
modifications of the ependymal cells which enter into them
leave little room to doubt that they are glandular in nature.
Indeed, the present tendency is to refer to these structures as
chorioidal glands, thus deputing to them a definite, secretory
function in relation to the cerebrospinal fluid. Even the older
conceptions of the chorioid plexuses recognized this physio-
logical possibility in connection with the plexuses.

The morphological fact concerning the first and most cephalic
of the three arches in the pineal region discloses a predominant
tendency for its derivatives to give rise to glandular structures,
while, on the other hand, there is no evidence that it has ever
been engaged in definite neural mechanisms.

The structure which forms the boundary between the prevelar
or paraphyseal arch and the postvelar arch is the velum trans -
versum. Like the paraphyseal arch, it attains its greatest con-
spicuity in the lower vertebrates and in the higher forms becomes
less prominent. In mammals its appearance is most pronounced
in the embryonic period from which time it becomes progres-
sively reduced, being present in the adults of most orders as a
more or less well-marked rudiment. In most classes of verte-
brates it becomes associated with a dense mesenchymatous in-
vasion which results in a fairly rich vascularization. This com-
bination of ependymal cells and blood vessels often takes the form
of a plexus, and when such is the case the velum transversum
aligns itself with the structures derived from the paraphyseal
arch in the absence of any definitely neural elements and the
tendency toward glandular formation.

200 FREDERICK TILNEY AND LUTHER F. WARREN

The middle or post velar arch (so called by Minot277) in the
pineal region has also been designated the Zirbelpolster by
Burckhardt,17 the post paraphysis by Sorensen,361 the dorsal sac
by Goronowitsch,168 and the roof . of the parencephalon by
Kupffer.226 This structure, with few exceptions, forms a prom-
inent element of the pineal region throughout the vertebrate
series. In cyclostomes it is present as a simple membranous
sac with scant vascularity of its own, although in close approxi-
mation with the highly vascular mesenchyme dorsal to it. In
selachians it is usually somewhat more extensive yet similar in
its structural details. In ganoids it becomes immensely ex-
panded as shown by Balfour,11 Huxley, 1<n Wiedersheim,426
Goronowitsch,153 Wilder,428 and Kingsbury.204 Herrick178 describes
the dorsal sac as a pouch lined with a single row of ependymal
cells with long cilia which appear to be of the epithelial, secre-
tory type. It is highly vascular in these fish. In teleosts, on
the other hand, it is not always prominent, In Opsanus, Terry392
found that the dorsal sac was small and perhaps disappeared
altogether. In some teleosts, as in ganoids, the postvelar arch
is not only highly vascular, but presents ridges, secondary folds,
and diverticula. In amphibia, reptiles, and birds, the postvelar
.arch becomes definitely associated with the formation of the
•chorioid plexuses, and it does, in fact, contribute the epipthelial
elements to the chorioid plexus of the diencephalon. With the
advent of the corpus callosum in mammals the dorsal sac or
postvelar arch becomes somewhat overshadowed, due to the
introduction of the transverse commissure which lies above and
tends to flatten it. It, however, loses none of its tendency to
participate in the plexus formation, which latter in mammals
attains a greater development than in many of the lower forms.

This element of the pineal region, therefore, is to be associated
with the paraphyseal arch in its tendency toward specialization
From the lowest vertebrates upward through the phylum it
manifests no attempt toward the development of sensory or
other definitely neural elements, while the entire trend of its
evolution reveals a glandiferous potentiality.

THE PINEAL BODY 201

The postvelar arch is separated from the caudalmost or epi-
physeal arch of the pineal region by a shallow invagination of
the diencephalic roof, which usually contains commissural
nerve fibers. This is known as the superior commissure or
commissura habenularis. In some forms, as in amphibia, it is
associated with a small, somewhat thickened area of the roof in
which the histological elements are largely neuroglia. This is
the pars intercalaris anterior. Although the structure, or its
homologue, occurs in such a limited number of animals, its
recognition as a distinct part seems advisable in the description
of this area of the brain. In cyclostomes, prosaurians, and
saurians, the superior or habenular commissure seems to be
connected with the parapineal or parietal nerve and, perhaps,
through this relation is brought into connection with the end-
vesicle of the parapineal organ. If such is the case, it may well
be that this commissure in cyclostomes, in prosaurians, and in
saurians is related to an organ of special sense. In this light
the superior commissure must be accounted as engaged in the
organization of a specialized neural mechanism, and thus be-
comes the first of the structures encountered in the pineal region
to show this tendency in differentiation. The significance of the
pars intercalaris anterior is not altogether clear, although it is
possible that it may represent a residue of an unutilized susten-
tacular area developed in the interest of the commissural forma-
tion. The presence in it of a few nerve fibers would seem to
substantiate this view.

The caudalmost or epiphyseal arch is by far the most complex
of the three arches in the pineal region. In order that its de-
scription may be comprehensive enough to include all verte-
brates, a number of different elements are to be recognized,
either as appearing in the embryo or giving rise to definite adult
structures whose composit may, for convenience, be termed the
epiphyseal complex. This complex, then, consists of two princi-
pal organs, namely, the pineal organ and the parapineal organ.
Each of these organs is in turn susceptible of subdivision into
certain portions as follows:

202 FREDERICK TILXEY AND LUTHER F. WARREN

1. Pineal organ. 2. Parapineal organ.

a) Proximal portion. a) Proximal portion.

6) Stalk. 6) Stalk.

r) End-vesicle. c) End-vesicle.

Of all of those parts the proximal portion of the pineal organ
is phyletically the most constant, occurring in all classes of
vertebrates. The stalk and end-vesicle of the pineal organ
are much less constant, for they cease to appear in ophidians
and are absent in all the forms higher than the snakes. The
parapineal organ as a whole is limited to but a few classes of
vertebrates. It is prominent only in cyclostomes, in prosaurians
and saurians. It is rudimentary in ganoids and teleosts. It is
developmentally transitory or entirely absent in selachians,
amphibia, ophidians, chelonia, crocodilians, birds, and mammals.

Considered, for a moment, quite apart from the inferences
which may be drawn from the intrinsic structural characters of
the epiphyseal complex itself, there is one outstanding feature
of unquestionable importance, namely, the genetic association of
this complex with a series of organs which under no conditions
have manifested a tendency to become specialized in the interest
of definitive neural mechanisms, but which, wherever differ-
entiated, have given rise to glandular tissue.

The caudalmost element in the pineal region is the posterior
commissure. It is, perhaps, not definitely settled that this
assignment of the commissure to the interbrain is in all respects
justifiable. If, however, it is to be accounted as a structure of
the pineal region, the function of the commissure appears to be
related to a specialized portion of the pineal organ, namely, the
end-vesicle, with which latter the posterior commissure is said to
be in connection by means of nerve fibers. Admitting, for the
moment, the correctness of the morphological and physiological
interpretation given the subcommissural body by Dendy and
Nicolls,88 the structure may tentatively be considered as a
part of the pineal region. Its function, apparently, is in sonic
way connected with the fiber of Reissner and the entire organ
thus :i— oriutod with equilibration. Both of these elements,

THE PINEAL BODY 203

constituting the caudalmost constituents of the pineal region,
are obviously specialized as neural mechanisms in the interest of
special sense receptors. The pars intercalaris posterior has, no
doubt, the same functional significance as the anterior inter-
calated area associated with the superior commissure.

From a review of the several structures associated with the
epiphyseal complex in the pineal region, it is clear that the
majority of them when differentiated at all give rise to glandular
organs, while those which participate in neural mechanisms are
not only in the minority, but constitute a relatively small portion
of this area in the brain. Thus the paraphysis and paraphyseal
arch as a whole, the velum trans versum, and the post velar arch
are genetically glandiferous, while the superior commissure and
posterior commissure alone bear any apparent relation to neural
activity.

In view of these facts, it would seem that whatever the func-
tions of the epiphyseal complex may be, the morphogenetic
impulse imparted to it from a region of the brain so preponder-
atingly glandiferious in its constituents could not fail to have
a profound influence upon the evolutional adaptation of the
epiphysis. Yet, in spite of the illumination which this genetic
association of the epiphyseal complex with definitely glandular
structures seems to shed upon its inherent tendencies in differ-
entiation, it must be in the intrinsic characters of the complex
itself that the solution of its problem is ultimately to be sought.

2. Evidence based on the gross morphology of the epiphyseal

complex

a. Phyletic constancy. If such evidence as may be obtained
from the gross morphology of the epiphyseal complex is taken
into account, a number of reasons may be advanced to show
that it is quite impossible to conceive of the pineal body as a
vestigial structure. These reasons seem so cogent as to place
upon the arguments which would refute them an unusually
heavy burden.

204 FREDERICK TILNEY AND LUTHER F. WARREN

The most significant feature with reference to the functional
activity of the pineal body appears to be the fact of its marked
phyletic constancy. Certainly, a structure which is marked for
regression or in which it is claimed that the evidences of regres-
sion may easily be found, would scarcely show such remarkable
tenacity throughout the phylum. Its occurrence in cyclostomes,
in all the fish, in amphibians and reptiles, in birds and mammals
reveals it as a structure which must have been called into being
in response to some definite demand, for why, otherwise, should
all of these classes of vertebrates so constantly present this
morphologic condit ion ?

It is, perhaps, laying overmuch stress upon the phyletic
constancy of the epiphyseal complex to draw from these facts
alone the inference that it must be a physiologically active
organ. Its reported absence in the Myxi no-ids, in Torpedo
ocellata, and Torpedo marmorata as well as in Crocodilia would
seem to call into question the full value attached to the argu-
ment of its otherwise general constancy. On the other hand, it
must not be overlooked that in the history of the observations
devoted to the pineal body, a relatively large number of investi-
gators have reported the absence of the epiphysis in one form
or another, only -to have their error corrected by subsequent
research and the presence of the organ clearly demonstrated.
By far the greater majority of observers in the morphology of
this portion of the brain are to-day of the opinion that the
epiphyseal complex as a whole or in some of its parts exists in
all vertebrates. It is certainly pertinent to the reported absence
of the organ in the forms mentioned to recall Kicld's203 observa-
tion that the conditions in Torpedo need further review before
final acceptance of the statement that the epiphysis is absent in
these forms. The same also applies to Crocn<lili<i, and until
this order has been more extensively examined, much reserva-
tion should be made in concluding that the pineal body is absent
in these reptiles. Again, Kit Id's'-'1" contention with reference to
the Myxinot'ds adds another view which would render less serious
the reported absence of the epiphysis in the forms mentioned.
According to Kidd, it is not surprising that in N ii.riin>i<lx the

THE PINEAL BODY 205

epiphysis is wanting, since these are considered, by most author-
ities, as degenerated forms.

With these exceptions, then, so much in the minority, this
negative evidence should be accepted with much hesitancy.
In fact, the phyletic constancy of the epiphyseal complex is so
pronounced as to render the total absence of the organ in Myxi-
noids, Torpedo, and Crocodilia open to doubt.

b. Phyleiic variations and morphologic specialization. If the
constancy already considered lends itself to the weight of evi-
dence in favor of the supposition that the pineal body is a func-
tional organ, then even more will the phyletic variations and
morphologic specializations which present themselves in this
organ support the view that the epiphysis is not a vestige, but
plays some physiologically definite role.

Certainly, when the marked specialization in the epiphyseal
complex in the various orders of vertebrates is taken into ac-
count, it is difficult to escape the conclusion that such modifica-
tions must have been in the interest of definite adaptations.
If these specializations referred to were indefinite or diffuse, it
might still be a question whether the processes were actually in
the interest of adaptation; but when, as is the case, form after
form shows such a high state of differentiation, such a definite and
discrete specialization, there seems to be little room for doubt
that a process of adaptation has been carried forward in order
to satisfy the demands for the development of specialized organs.

On the other hand, it cannot be denied that even such discrete
differentiation as the epiphyseal complex presents in many
forms, may represent but the rudiments of an adaptive process
which in some extinct forms, or perhaps even in some of the
proto-vertebrates, may have attained their functional consum-
mation only to impart an impulse in this direction to those verte-
brates which show the most definite specialization in the pineal
organs.

In this sense, all of the differentiation of the epiphyseal com-
plex throughout the vertebral phylum expresses an inherent
attempt to consummate the formation of organs which have
been essential in extinct forms or in the ancestors of the verte-

206 FREDERICK TILXEY AXD LUTHER F. WARREX

brates. This contention, while it must have its place in the
discussion, seems to lose force in view of the special development
of the pineal organ in certain vertebrates. Thus, in cyclostomes
there is present, to a degree seen in no other vertebrates, a
development of the major constituents of the epiphyseal com-
plex. That is to say, both the pineal organ and parapineal
organ attain a degree of differentiation which at least justifies
the supposition that one, if not both of them have functional
activities of a visual nature. The presence in these forms of a
well-marked retinal structure, seen in the pineal organ as well
as in the parapineal organ, an end-vesicle containing a syncytial
structure comparable in many respects to the vitreous, a pig-
ment-free, ectal wall enclosing the end-vesicle and resembling a
lens, together with a bundle of nerve fibers connected with the
posterior commissure in the case of the pineal organ, and the
superior commissure in the case of the parapineal organ, con-
stitute irrefutable evidence of morphological specialization
adapting the organ to photo-receptive, if not visual purposes.
This supposition is further borne out by the fact that the organs
in their development grow rapidly away from the roof of the
brain and ultimately take up a position which, from its relation
to the surface of the body, affords certain epiphyseal structures
the best opportunity of becoming distance receptors. From the
striking position which the pineal and parapineal organs hold in
the vault of the skull, lodged as they are in a deep fossa, it would
seem evident that they have become so situated that they might
the more readily receive sensory impulses impinging upon the
surface of the head.

That this visual or photo-receptive tendency in the selachians,
ganoids, and teleosts should almost altogether disappear, al-
though the pineal organ itself remains as a conspicuous struc-
ture, would speak in favor of a pluripotentiality in the differen-
tiation of the epiphyseal complex. It is certain that in the
higher fish there is no evidence pointing to the development of
anything resembling the visual structures observed in cyclo-
stomes. In selachians the parapineal organ is entirely absent :
the pineal organ, <n 1 he other hand, is a large and prominent

THE PINEAL BODY 207

structure presenting a proximal portion, a prolonged stalk, and
a fairly well marked end-vesicle. No tendency, however, is
observed toward the development of a photo-receptive appara-
tus. The thickened proximal portion communicates directly
with the ventricle on the one hand, and through the stalk with
the end-vesicle on the other. The fact that this latter portion
of the pineal organ is lodged in a deep fossa of the skull and thus
brought into close relation with the epidermis, would favor the
belief that in this structure may be observed the arrested or
abortive effort toward the formation of a physiological organ.
That this organ, however, deprived of the opportunity to reach
such a goal in its differentiation, should remain so prominent a
structure connected with the brain, would seem to refute the
conception that it is a mere vestige or rudiment; indeed, it
seems to compel the belief that it exists in the interest of some
other function as yet not entirely clear.

When, however, the finer histological structure of the pineal
organ in selachians is discussed, it may be possible to disclose
evidence which will at least suggest, that the structure in these
forms is functionally active. The point which the gross mor-
phological conditions in selachians does lay emphasis upon is the
presence of so prominent a structure, showing no evidence in
itself of retrogression and yet quite devoid of such specializa-
tion as would connect it definitely with visual function.

In the teleosts, the observation made with reference to the
selachians assumes even more importance, for here the pineal
organ shows a marked specialization which is entirely contrary
to the lines of differentiation followed in the development of a
visual organ. In most of the teleosts the pineal organ presents
a small proximal portion, a relatively short stalk, and a volumi-
nous thick-walled end-vesicle. The general follicular appear-
ance of the end-vesicle, together with its relatively large size
and the fact that it has neither migrated to such a great distance
from the roof-plate of the interbrain nor come to occupy a defi-
nite fossa in the vault of the skull, all go to disprove any inherent
tendency in the structure to differentiate as a visual organ. In
many teleosts a small parapineal organ develops, but never

208 FREDERICK TILNEY AND LUTHER F. WARREN

reaches dimensions comparable with the pineal organ. As in
the case of the selachians, the histology of the pineal organ of
the teleost will prove helpful in the interpretation of its function.

Thus, in the four great classes of fish, cyclostomes, selachians,
ganoids, and teleosts, the epiphyseal complex shows a remark-
able variation in its specialization, and while the tendency to
develop visual or photo-receptive structures is marked in the
cyclostomes, it is suspended, if not entirely absent, in selachians,
ganoids, and teleosts.

In the latter forms, however, the epiphyseal complex is so
conspicuous an element of the brain as to make the conclusion
that it is without function a difficult one to maintain. For these
mi sons, it would seem justifiable to conclude that the epiphyseal
complex is pluripotential in its specialization and that while it
may be vested with the possibility of giving rise to a visual or
photo-receptive apparatus, it may and does become differ-
entiated as organs having some significance other than sensory.

Still greater modifications present themselves in the amphibia,
for in these forms the pineal organ shows an even more marked
differentiation than any of the other lower classes. The para-
pineal organ does not develop in urodela or anura. When, how-
ever, the structure of the pineal organ is considered, the fact
that it develops a proximal portion of such conspicuous dimen-
sions as to be secondary to the paraphysis in the roof of the
interbrain, from the free extremity of which there extends a thin
nerve filament connecting with an end-vesicle, it becomes clear
that the entire process of adaptation in this instance cannot be
in the interest of sensory function, for if that were the case,
why, then, should the proximal portion of the pineal organ
assume such conspicuity?

Stieda's37" interpretation of the end-vesicle in amphibia as a
frontal subcutaneous gland is, of course, quite untenable, since
the end-vesicle manifests by its position and connections some
obvious adaptation to sensory activity. Yet to its proximal
portion might well be attributed a glandular function, not
only because of its unusually large dimensions, but also because
of the position which it holds with reference to the third ventricle.

THE PINEAL BODY 209

If the argument bearing upon the pluripotentiality of specializa-
tion of the epiphyseal complex needed support or confirmation,,
this is found in the conditions of amphibians.

The evidence afforded by the reptiles goes, perhaps, as far
as may be deemed necessary to confirm the pluripotentiality of
the pineal organ and its derivatives. In the ancient and primi-
tive reptiles, including the prosaurians and saurians, there is a
tendency for both pineal and parapineal organs to attain remark-
able development. But in these forms, it is the parapineal organ
which assumes predominance in the development of a sensory
apparatus. In sphenodon and many of the lizards the parietal
or third eye reaches such a high state of differentiation as to
leave little doubt concerning its visual function. The well
marked optic vesicle, lodged in a parietal fossa and brought into
relation with the external epidermis by means of specialized cells,
affords incontrovertible evidence that this organ is adapted as a
distance receptor. The pineal organ, while it presents some
tendency towards the development of a visual organ, does, as a
matter of fact, fall far short of such attainment. Its end-vesicle
is smaller than in any of the other forms already considered.
Its stalk is shorter; on the other hand, its proximal portion has
assumed characters not as yet observed in the lower members of
the vertebrate series. So pronounced is the specialization of
this proximal portion that it needs no microscopic investigation
to disclose the marked differentiation of the structure. Its
walls are not only thick and convoluted, giving it a lobulated
appearance, but its diameters are greater than those of the
lower forms.

Upon passing to the more modern reptiles, including the
ophidians and chelonians, the tendency to specialization which
has previously been emphasized in this discussion, receives still
further accentuation. In these forms, the parapineal organ dis-
appears altogether and nothing remains to indicate that it ever
had existence in reptilia. There is no parietal fossa and no
specialization of the cutaneous surface in the head which might
even vaguely suggest the remnants of the parietal eye so con-
spicuous in the ancient reptiles. Yet, on the other hand, the

MEMOIE NO. 9

210 FREDERICK T1LNEY AND LUTHER F. WARREN

pineal organ manifests such marked alterations as to leave no
doubt that a process of specialization is going on in this struc-
ture. It is a much more voluminous organ having a greater
solidity and presenting only one of the three fundamental por-
tions observed in the pineal organ of the lower forms. The
end-vesicle and the stalk of the end-vesicle have disappeared.
The proximal portion alone remains to represent the epiphyseal
complex. It also manifests certain modifications in its relation
to the brain, since now it no longer communicates with the ven-
tricle through a canal. Furthermore, it has developed a shallow
hit (-run diato stem or stalk connecting it with the roof-plate.

The incept i< n of the process resulting in the formation of
the pineal peduncle is first witnessed in the sphenodon and
lacertilia. The conditions in birds and mammals show a still
further tendency along the lines of specialization first manifested
in ophidians, for, as in these latter forms, neither the parapineal
organ nor the end-vesicle or stalk of the pineal organ makes its
appearance. The epiphysis in many of the birds becomes a
solid organ with no canal connecting it with the third ventricle,
although in certain birds this canal is present. In mammals the
canal has never been observed and the pineal body presents
itself as a dense, solid structure in close proximity to the roof of
the interbrain or resting upon the roof-plate of the midbrain.

Another observation made by Kidd203 is pertinent in this con-
nection, to the effect that if nature is endeavoring to be rid of
the pineal body it has taken a remarkably long time imper-
fectly, if at all, to accomplish this end. The evidence that the
reptiles in the Palaeozoic era possessed a parietal eye is sub-
stantiated by the parietal foramen in these extinct forms, as
deiiMii-1 rated by Bashford Dean.82

All of this evidence concerning the phyletic variations and
morphologic specialization seems to justify the conclusion that
the epiphyseal complex is possessed of a pluripotentiality which
in a few forms has been realized as a more or loss diffuse visual
si met ure, but which fundamentally appears to be in the interest
of a differentiation whose functionl significance is not sensory.

THE PINEAL BODY 211

c. Relative constancy of the epiphyseal complex with reference
to other structures of the pineal region. The phyletic constancy
of the epiphyseal complex, when considered in conjunction with
the other derivatives of the diencephalic roof-plate, brings to
light a fact of no little significance. It has already been, shown
how constant the epiphyseal complex, either in its entirety or
in some of its parts, is in the vertebrate phylum, and this be-
comes further emphasized by the fact that this structure alone
of all the elements derived from the roof-plate presents such
undeniable constancy. If compared with one of the most con-
spicuous roof-plate derivatives, the paraphysis, the epiphyseal
complex stands out in marked contrast. The paraphysis is
present in its highest state of evolution in the middle of the
vertebrate series; that is to say, in amphibians and in older
reptiles. It is a conspicuous organ, showing but little differ-
entiation in cyclostomes and in fishes generally. In ophidians,
birds, and mammals it is absent. The inference which may be
drawn from these facts seems to be that the roof-plate of the
interbrain is capable of developing a structure which, when it no
longer subserves any purpose, ceases to exist. When the phy-
letic constancy of the epiphyseal complex is compared with that
of the paraphysis, it would seem evident that this very constancy
argues a demand on 'the part of the organ for the presence in the
animal of this complex or some of its parts.

To a less degree, the comparison in favor of the pineal organs
may be drawn with reference to the velum transversum, telen-
cephalic chorioid plexus, and dorsal arch. None of these show
such a marked tenacity as the epiphyseal complex, a fact which
but serves to emphasize the significance of the relative constancy
among the structures derived from the diencephalic roof-plate.

d. Relative constancy of the several parts of the epiphyseal com-
plex,.with the predominance of the proximal portion. Since each
organ of the epiphyseal complex presents three more or less
well-defined portions, namely, the proximal portion, the stalk,
and the end-vesicle, it would be interesting to note the relative
constancy of the several parts in the phyletic series in order to
ascertain, if possible, which of these is the most fundamental

212 FREDERICK TILM.V AND LUTHER F. WARREN

element in the complex. Both organs are well developed in
cyclostomes. The proximal portion of the pineal organ, al-
though present, is not conspicuous, but it is doubtful whether
any structure which may be designated a proximal portion can
be discerned in the parapineal organ. The stalks and end-
ve-icles are present and highly specialized. The stalks have
lost their original lumina and consist of two sets of nerve fibers.
Both end-vesicles are well differentiated.

In selachians the parapineal organ is entirely absent. The
proximal portion of the pineal organ is well marked, its stalk is
long and hollow, and its end-vesicle a dilated sac.

In ganoids and teleosts the parapineal organ is rudimentary;
in the embryo it presents a small proximal portion which subse-
quently becomes much reduced in size, rendering it difficult of
recognition in the adult. The stalk is short and slender and con-
tains no lumen. The end-vesicle is very small. The proximal
portion of the pineal organ shows a considerable dilatation and
is connected, by means of a hollow stalk, with an extensive
end-vesicle.

In amphibia the parapineal organ is absent. The proximal
portion of the pineal organ is a large, dilated sac whose lumen
communicates with the third ventricle. The stalk is reduced to
a slender nerve strand extending from the free extremity of
the proximal portion to the end-vesicle which lies immediately
beneath the skin in the region of the head.

In the primitive reptiles, including sphenodon and lacertilia,
the parapineal organ is p resent and shows a marked development.
In the embryo there is a prominent proximal portion, which,
however, becomes gradually reduced in size, and in the adult is
difficult to distinguish. The stalk of the parapineal organ
pre-eni- it -(-If in the form of a long slender fasciculus of nerve
libers which connects the superior commissure with aii-end-
veside. The pineal organ shows a, highly specialized proximal
portion which is large and convoluted. Its cavity communicates
with the third ventricle through a narrow canal. The stalk is
short and contains a cavity which communicates with the eiul-
vesicle at its distal extremity and also with the proximal por-

THE PINEAL BODY 213

tion. In ophidians and chelonians the parapineal organ is
entirely absent, and the only element of the pineal organ which
persists is the proximal portion which has become converted into
a more or less solid structure extending from the roof of the brain
dorsad" toward the vault of the skull. Similarly, in birds and
mammals, the only element of the epiphyseal complex which
may be recognized is the proximal portion of the pineal organ.
This, as in reptiles, is an organ of considerable density close to
the roof of the brain.

From these facts it will be seen that the proximal portion of
the pineal organ is the most constant element of the epiphyseal
complex, the next in point of frequency being the end-vesicle
and stalk of the pineal organ. It \vould seem, therefore, that the
proximal portion of the pineal organ should be considered the
fundamental element of the epiphyseal complex, and its struc-
ture would, therefore, demand particular attention. That this
element in the epiphyseal complex does show a marked tendency
toward specialization from the selachians to reptiles, birds and
mammals is convincing evidence that this structure is not to be
considered a vestige, for were such the case it would scarcely
manifest such a definite tendency toward specialization in the
processes of evolution.

e. The epiphy so-cerebral index. Not alone is the evidence
obtained from the comparative studies of the pineal body in
favor of its progressive specialization, but quite as much the
facts obtained from ontogenesis of the organ in man. We are
fortunate to possesss a careful series of observations made by
Cutore76 in which the weight of the brain as well as the wreight
of the epiphysis and the hypophysis have been recorded. These
statistics are based upon the observations ranging from the new-
born to the seventieth year of life. In all, twenty-five brains
were studied, and it would seem that from such material, limited
though it may be, some light might be shed upon the ontogenetic
evolution, upon the epiphysis in its relation to the rest of the
brain and also to a recognized endocrinal organ, the hypophysis,

If, as has been frequently maintained, the pineal body is a
vestige and of no functional significance, then the tendency for

214

FREDERICK TILXKV AND LUTHER F. WARREN

this organ should be to manifest the signs of regression through
the periods of growth in num. Or if, on the other hand, as is
thought to be the case by many, the organ is functional only
in the fetal and in the early postnatal stages, then the relative
weight of the organ to the rest of the brain should show an
alteration in its ratio, indicating a progressive retrograde process
taking place in its structural elements.

In ))]•< 'paring the figures of Cutore, in order most effectively to
assemble the facts necessary to this argument, his cases were
grouped in such a way as to constitute five more or less well-
drfined epochs of life.

1. Six examples of infante in the first year.

2. Five examples of infants in the second year.

3. Six examples of children from 3 to 14 years.

4. Five examples of adults from 15 to 25 years.

5. Three examples of adults from 60 to 70 years.

AVERAGE WEIGHT IN GRAMS

INDEX TO BRAIN

i

Epoch

Brain

Hypophysis

Epiphysis

Hypophysis

Epiphyais

1st

600

6.103

0.031

0.00017

0.00005

2nd

734

0.154

0.055

0.407

0.00007

3rd

1,105

0.262

0.100

0.00024

0.00009

4th

1,218

0.508

0.119

0.00040

0.00009

5th

1,125

0.500

0.130

0.00040

0.00010

It will be seen from these figures that of the three structures
considered, the average weight of the epiphysis alone tends to
increase constantly through the five epochs differentiated in
this study. The brain itself shows a constant increment in
weight from the first year to and through the twenty-fifth year,
but in the fifth epoch, from sixty to seventy years, there is an
apparent decrease of nearly 100 grams in brain weight. The
increase in the hypophysis runs parallel to that of the brain,
for up to the fourth epoch and including it the increment in
weight in the hypophysis is constant, but in the fifth epoch,
from sixty to seventy years, the figures seem to indicate a defi-
nite decrease in weight. The indices expressing the epiphyso-

THE PINEAL BODY 215

cerebral and hypophyso-cerebral ratio bear out this observa-
tion and definitely indicate an increase in the proportion between
the brain and the epiphysis from the first year of life to the
fifth epoch, between sixty and seventy years. If compared with
the conditions observed in a definitely known endocrinic organ,
the hypophysis, it will be observed that in the first period the
weight ci the pineal bcdy is 30 per cent of the hypophysis; in
the second epoch it is also 30 per cent; in the third epoch it is
35 per cent, an increase which is of much importance and inter-
est in this connection, since it is the general supposition that the
gland has its greatest functional activity during this time of
life. - In the fourth epoch the epiphysis is 22 per cent of the hypo-
physeal weight, while in the fifth epoch it is 25 per cent.

It should be borne in mind, while considering these figures,
that the hypophysis is a compound organ, being made up of a
neural portion in addition to an element derived from the oral
ectoderm. Its greater weight, therefore, is in part, at least,
explained by its non-glandular neural portion, and its total
glandular weight would be represented by a fraction only of this
total. In this light, the proportion between the epiphysis and
the hypophysis would be materially changed, and while it is
impossible to say exactly what ratio the neural portion of the
hypophysis bears to the glandular portion, it would be safe to
assume that the proportion is as 1 : 2.

' From this standpoint, the figures concerning the epiphysis
assume more definite significance and would seem to point
strongly to the supposition that an organ destined to become
regressive would scarcely keep pace so constantly in its weight
increment with an organ like the hypophysis of known endo-
crinic function. The figures cited are suggestive in another
sense, namely, they would seem to show that the activity of the
pineal organ, should such be accredited to it, does not cease at
any particular period of life, and that while there may be reason
to believe that the greatest functional activity is present in the
third epoch, between the third and fifteenth years, there are
good reasons to believe that the organ does not cease to perform
its functions even up to the time of old age.

216 FREDERICK TILNEY AND LUTHER F. WARREN

/. Resistance to tfte encroachment of the corpus callosum. An-
other characteristic in the ontogenesis of the epiphysis, especially
in mammals, speaks against the possibility of its being a vestige
and indicates in it a tenacity as a morphologic structure so
marked as to suggest the probability of some inherent functional
activity. With the advent of the commissural fibers whose mas-
sive collection goes to make up the corpus callosum, the maniT
malian brain takes on a character not observed in the lower
forms. The gradual extent of this great interhemispheral com-
missure in a caudal direction subjects the entire roof of the
diencephalon to new conditions. The influence of these new
conditicns is readily seen in the flattening of the dorsal sac .and
the reduction of the paraphyseal arch. Yet, even in the in-
stances in which the corpus callosum extends far enough caudad
to reach the midbrain, the epiphysis withstands its encroach-
ment and gives evidence of a resistive adaptation against the
pressure of the new structure. It seems fair to presume that if
there were vested in the pineal body an inherent tendency to
retrograde, under the pressure of this newly developed mam-
malian structure which has so uniformly altered the configura-
tion of other elements in the diencephalic roof -plate, the epiphysis
itself must have given evidence of much less resistance or per-
haps have succumbed altogether. Its evident effort at adapta-
tion has already been referred to in the classification of the
epiphysis in mammals which, according to Cutore,76 shows a
disposition on the part of the organ to accommodate itself to
the presence of the corpus callosum, in some forms being retro-
callcsal in position, in others supracallosal, and still again main-
taining itself in all its morphologic intactness in a distinctly
subcallosal position.

If the epiphysis is to be considered a vestige, in view of the
morphologic evidence above summarized, it seems apparent
that the lim-dm of proof rests with those making the claim that
it is a rudimentary structure. To maintain this position they
must meet with some well-sustained objections the following
e-i.->l>li>hed facts:

THE PINEAL BODY 217

1. The phyletic constancy of the epiphysis.

2. Its phyletic variations and morphologic specializations.

3. Its relatively greater phyletic constancy with reference to
other structures in the pineal region.

4. The phyletic predominance of the proximal portion of the
pineal organ.

5. The evidence of its progressive specialization in ophidians,
birds, and mammals.

6. The increase of the epiphy so-cerebral index from the
earliest stages to the latest periods of life in man.

7. The resistance to the encroachment of a prominent neo-
morph in the mammalian brain such as is the corpus callosum,
whose presence has produced" such a marked alteration in the
other constituents of the diencephalic roof -plate.

3. Evidence based on the histology of the epiphyseal complex

From the comparative histology of the epiphyseal complex,
it becomes evident that specialization in these organs has fol-
lowed two main lines: First, the structures have either differ-
entiated in the interest of forming visual organs or, second,
they have given rise to glandular itissue. In some instances,
both of these tendencies may be observed, that is to say, in
certain species the differentiation has been in the interest of
visual apparatus in one part of the epiphyseal complex, while in
another part, distinct glandular tendencies are apparent. It
seems advisable for the purpose of obtaining as comprehensive a
view as possible of the histology of this portion of the brain to
consider the leading features of the finer structure in the pineal
body of each of the classes of vertebrates.

Histological evidence in cyclostomes. The striking histological
features in cyclostomes are the specializations in both pineal and
parapineal organs in the interest of forming visual structures.
The end-vesicle of the parapineal as well as the pineal organ
presents a retina. This structure in the pineal organ contains
cells of a distinct rod-like shape which have, therefore, been
designated the rod cells. Other cellular elements are also ob-

218 MM.UKHICK TILXEV AND LUTHER F. WARREN

served in the vent ml wall of the end-vesicle which appear to be
of a sensory nature. Certain large elements have been recog-
nized in the deeper layers of the tissue and by some authorities
are considered to be ganglionic cells. In addition, there are cells
of an ependymal nature or modifications of the latter which give
the impre>si«.n of neuroglia tissue. There can be little question
that the retina of this organ is well enough defined to deserve
that designation. Whether it is actually functional as a visual
organ is not altogether clear, for the relation of the pineal eye in
cyclostomes to the surface of the head does not afford the most
advantageous conditions for a distance receptor.

The end-vesicle of the parapineal organ closely resembles the
finer structure in the corresponding part of the pineal organ.
There are, however, certain differences which are more those of
degree than of kind. The rod cells, such conspicuous elements
in the pineal organ, are less well defined in the parapineal organ
and so also are the ganglionic cells.

The differentiation of the dorsal wall of the end-vesicle in the
pineal as well as in the parapineal organ manifests a tendency
toward lens formation, for in both cases the cells in this region
are entirely pigment-free and give rise to a translucent structure
known as the pellucida. Further evidence of the visual adapta-
tion observed in the end-vesicle of the two structures of the
epiphyseal complex is the fact that the cavity of the vesicle is
filled with a coagulum in the meshes of a delicate syncytium, a
structure which so closely resembles a primitive vitreous that it
may be regarded as analogous, if not homologous to that struc-
ture. The presence in the retina of a widely distributed white
pigment lends the necessary opacity to the visual membrane.
Both end-vesicles contain thjs pigment; its presence serves
further to convey the impression of differentiation along visual
lines.

The si;ilks of both the pineal and parapineal organs bear a
certain amount of confirmatory evidence in favor of the belief
that the epjphvseal complex in cyclostomes has made the at-
tempt at visual adaptation. Nerve fibers are uniformly ob-

* THE PINEAL BODY 219

served in the stalks; those coming from the pineal end-vesicle
terminate in the posterior commissure, while those seemingly in
connection with the parapineal end-vesicle end in the habenular
commissure. Some collateral evidence 'is afforded by the appear-
ance of a parietal cornea, a fiberless tissue which surrounds the
pineal and parapineal end-vesicles.

All of these histological facts, based upon the observation of
cycle stomes, indicate what may be considered an abortive yet
a well-advanced attempt to the formation of two eyes. There
is no evidence of glandular formation in any part of the epi-
physeal complex in cyclostomes.

Histological evidence in selachians. The characteristics of finer
structures, so conspicuous in petromyzon and its congeners, is
strikingly absent in the next higher order, the selachians. In
consequence of the apparent lack of differentiation, the entire
parapineal organ is absent, while the pineal organ, although
conspicuous for its size, shows no tendency toward the formation
of a retina, pellucida, white pigment, or nerve fibers. It is a
question whether the pineal organ in selachians should be con-
sidered as a primitive organ or as one in a stage of retrogression.
The walls of the end-vesicle are made up exclusively of epen-
dymal cells and contain neither spindle nor rod cells. In one
form, Scyttium, Galeotti140 described a peculiar appearance of
the cells of the end-vesicle which seemed to indicate a secretory
function. This conclusion of Galeotti's depends on the appear-
ance of fuchsinophile granules not only in the nuclei of the cells,
but scattered diffusely throughout the cytoplasm. Studnicka391
also recognized these cells and, wrhile he was unwilling to attrib-
ute any definite function to them, he was of the opinion that they
could not be secretory in their nature.

It is apparent, therefore, in passing from the cyclostomes to
the selachians that there is a striking absence of any visual
differentiation or any tendency in this direction, while the
presence of certain histological characters in the cells furnishes
evidence pointing to a possible glandular formation in the end-
vesicle of the pineal organ.

220 FREDERICK TILNEY AND LUTHER P. WARREN

Histological evidence in ganoids. The pineal organ alone
develops in ganoids, although in a single form, namely, Amia,
an abortive parapineal organ makes its appearance. The end-
vesicle of the pineal organ in ganoids generally shows some
tendency toward the development of a retinal or pellucidal
layer, although neither of these is well marked. Studnicka,391
as the result of his studies upon ganoids, does not believe that
there is any evidence of glandular activity in the end- vesicle
or proximal portion which is at all comparable to that of the
corresponding parts in selachians. On the other hand, he does
not deny that there may possibly be secretory function in the
pineal organ of ganoids.

Histological evidence in teleosts. The epiphyseal complex in
teleosts differs from that in selachians and ganoids in being a
much larger structure. The end-vesicle, furthermore, mani-
fests, in nearly every species, a pronounced tendency toward the
convolution of its walls. Not only is this process apparent
upon the surface, but section of the vesicle shows it to consist
of many folds and diverticula, all of which give to it the appear-
ance of a tubular gland in communication with the third ven-
tricle by means of a long hollow stalk. Galeotti140 in Leuciscus
found evidence of secretory activity in the presence of fuch-
sinophile granules similar to those described by him in selach-
ians. The product of this secretion, he thinks, is delivered to
the lumen of the end-vesicle and thus to the ventricle of the
diencephalon. Studnicka391 observed cells having a similar
appearance, and although he did not commit himself definitely
as to their nature, he nevertheless expressed the belief that the
organ is not entirely a gland. Some nerve fibers of the stalk
seem to represent a rudimentary pineal nerve.

Histological evidence in amphibia. The first recognition and
description given by Stieda37'-' in which he called the end-vesicle
a front ;tl subcutaneous gland was evidently a misinterpretation
of the conditions in amphibia. The end-vesicle in these animals
is fairly well developed, presenting a retina and lens which,
although clearly recognizable as such, have attained scarcely
more than an abortive state in their development. A long

THE PINEAL BODY 221

slender stalk made up almost exclusively of nerve fibers con-
nects this organ with the tip of the proximal portion and con-
stitutes a nervus pinealis, in the strict sense, which terminates in
the posterior commissure. Galeotti140 in Spelerpes fuscus
observed evidence of secretory activity, and this he also found in
Bufo and Rana. The evidence of secretory activity depended
upon the appearance of fuchsinophile granules in the cytoplasm.
Studnicka,391 following Galeotti, found, as he had previously
observed in selachians and teleosts, many cells in adult amphibia
containing cytoplasmic granules. These he interpreted as cells
having a sensory nature. Galeotti based his belief of secretory
activity in the pineal organ not merely upon the presence of
fuchsinophile granules, but quite as much upon epithelial char-
acters of the cells which were arranged in alveoli, thus giving
the end-vesicle and the proximal portion a glandular appearance.

It is apparent from this evidence that amphibia in general
present a very abortive attempt toward the formation of retinal
and lenticular structures, while the end-vesicle and the proximal
portion of the pineal organ both show some evidence of glandu-
lar formation.

Histological evidence in reptilia. The finer structure of the
epiphyseal complex in the primitive reptiles, including Spheno-
don and lacertilia, shows that in these forms the parapineal
organ attains its highest differentiation as a visual structure.
The pineal organ, however, shows no tendency whatsoever in
this direction, while, on the other hand, its proximal portion
affords many indications that its differentiation has been along
glandular lines. In ophidia and chelonia the proximal por-
tion of the pineal organ alone persists and has the appearance
of a highly vascular, richly branched, tubular gland. The
structure generally known as the pareital eye is a prominent
morphological feature in primitive forms of reptiles. It is
absent in certain geckonidae and in a number of agamidae. It
attains its greatest differentiation in Sphenodon and here pre-
sents a well marked retina, lens, vitreous, cornea, and nerve, the
latter relating to the ganglion habenulae. The accessory struc-
tures related to the parietal eye, including the cornea, parietal

2'2'2 P^REDERICK TILXKV A XI) LUTHER F. WARREN

fossa, and parietal spot, all give evidence of the most complete
adaptation for visual function.

Smdnicka-'"1 believes that the rich capillary blood supply in
ophidia speaks in favor of the glandular nature of the organ,
its secretion being contributed to the blood stream. In chelonia
the cellular elements are mostly ependymal and neurogliar and
no nerve cells or nerve elements are found. There is, however,
no clear evidence of the secretory nature of the epiphyseal com-
plex in these forms.

The conclusions which may be drawn with reference to reptiles
seem to indicate that in the primitive forms the parapineal organ
assumes the highest differentiation which it attains as a visual
structure. There is some evidence that the pineal organ, even
in the animals, manifests a tendency toward glandular forma-
tion. In ophidians, however, there can scarcely be a doubt
that the proximal portion of the pineal organ is the only element
which persists and that it has a definitely glandular structure.
This is probably true also in chelonians. The pineal gland in the
snake and turtle probably contributes its secretion, to the blood
stream, but may also impart a portion of it to the cerebrospinal
fluid. The more recent reptiles manifest no disposition on the
part of the epiphyseal complex to develop any sensory or other
type of neural mechanism.

Histolog-ical evidence in birds. The conspicuous change in the
epiphyseal complex noted in the transition from the primitive
reptiles to those of more recent history is strikingly emphasized
when the conditions in this region of the brain in birds are
reviewed. Here, as in the snakes and turtles, there is com-
plete suppression of the parapineal organ, and that tendency
toward the differentiation of a visual apparatus which seems to
have reached its height in Sphenodon, has so far receded as to
leave no indication in birds of its earlier existence. This histo-
logical feature of itself is highly significant, but when taken in
conjunction with the appea ranee offered by the finer structure of
the pineal body in birds, it seems to set all doubt aside as to the
inherent tendency of the epiphyseal complex along its major
of differential ion. In every species of birds which has so

THE PINEAL BODY 223

far come under observation, the differentiation in the pineal
body has been in the interest of glandular formation. This
evidence is not alone to be found in the character of the cells
which compose the body, but even more in the arrangement of
these cells whose alveolar patterns constitute irrefutable reasons
for regarding the epiphysis as a true gland in birds.

Three types of this gland are found in the avian forms, namely,
1) the tubular type, in which the secretion is delivered to the
ventricular system; 2) the endocrinic type, in which the secre-
tion reaches the blood stream, and 3), a mixed type, partaking
of the character of each of the former varieties. This evidence
afforded by birds is so conclusively in favor of the glandular
nature of the epiphysis as to leave no grounds for dispute. •

Histological evidence in mammals. It is perhaps in mammals
that the most extensive observations have been made with
reference to the histology of the pineal body. Indeed, it is in
these animals that the greatest variety of opinion has been
expressed. It would seem advisable to take into account these
different views concerning the histological character of the organ.
A large group of investigators adheres to the belief that the
pineal body is a blood vascular gland. This group includes,
among others, Valentin,403 Faivre,114 Leydig,231 Bizzozero,31
Galeotti,140 Constantini,71 Cutore,76 Galasescu-Urechia,137
Krabbe,217 Biondi,49 and Kidd.203 Jordan,199 although he does
not advocate the improbability of glandular formation, believes
that the organ is essentially neural in its structure.

Several investigators maintain that the epiphysis in mammals
consists exclusively of neuroglia. Among these are Cionini,66
Edinger,103 and Weigert.418 Mihalkovicz274 believed that the
cellular consistency of the pineal body in mammals was exclu-
sively of the ependymal type. Those of another group assert
that the epiphysis resembles a lymph gland. Of this opinion are
Schwalbe,348 Henle,171 Ellenberger110 Mingazzini,276 and Lord.249

Although it has been frequently claimed by many writers
among both the early and recent workers in this field that the
epiphysis is a vestige, it is interesting to note that no suggestion
of such a possibility is made by any of the authorities just

FREDERICK TILNEY AND LUTHER F. WARREN

cited. This is of particular significance because this list in-
cludes the names of those who have given the most extensive
attention to the histological character of the epiphysis in
mammals. Milhalkovicz'274 conception of the histology of the
pineal body seems hardly tenable, for it requires little study
covering a number of different mammalian forms to become con-
vinced that the cellular elements entering into the epiphysis
have nothing in common with the ependymal cells. Even
though it may be admitted that a certain number of the cellular
constituents of the epiphysis are ependymal in type, it cannot,
in the light of our present knowledge, be held that the organ is
made up exclusively of this type of cells.

On the other hand, it is not possible to acceed to the. conten-
lion of those who uphold the idea that the epiphysis is similar
t<» lymphatic glands. Not only does the character of the chief
cellular elements in the pineal body of mammals make this
position seem untenable, but even more does the arrangement
of these cells point away from the supposition that this is in
any sense lymphoid in character. Few cells in the body are
more conspicuous for their histological character than the chief
or parenchymatous elements of the mammalian epiphysis.
The large and centrally placed nucleus, the extensive and glan-
dular cytoplasm mark these cells so definitely that they may be
recognized without any difficulty even in those instances when
they become ectopic because of such migration as not infre-
quently results from tumor formation in the pineal body.

Our own work in this regard is illustrated in the figures which
show the character of the pineal gland cells in Macropus <//'</ ///,
Zul»/>li«x, Camelus dromedarius, Capra hylocrius, Lepus, ^i////n
.SV/////-//X, and in man. Furthermore, our observations in the
ontogenesis of the epiphysis in Felis domestica and in man,
illustrations of which are given in figures 91 and 92, show that
in the early stages of differentiation the nuclei of the ependymal
(•' I!- are so large and the cytoplasm so scanty that they give
the impression of lymphoid tissue, but in the later stages the
cytoplasm increases so considerably in amount that it is no
1< 'Hirer po-ible to conceive of these cells as lymphoid in char-

THE PINEAL BODY 225

acter. In fact, they have in the later periods of fetal and early
postnatal life all the appearances usually associated with glan-
dular cells. As compared to the cells in the glandular portion
of the hypophysis, the size of the pineal cells is two or three
times as great. This difference in size affords a striking point
of differentiation in those pathological conditions in which the
pineal cells in the course of tumor formation have migrated into
and through the posterior lobe of the hypophysis and invaded
the pituitary gland. The contrast is so marked as to present
no difficulty in the identification of the two varieties of cells.
That the epiphysis is made up of neuroglia cells in large part,
if not entirely, has been the contention of several observers.
The presence of short, branching fibers in close proximity to the
pineal cells has seemed to be the basis for this. On the other
hand, if the pineal cells in mammals are to be regarded as neu-
roglia, it must be granted that . they are certainly unlike the
neuroglia cells observed in other parts of the central nervous
system. Dimitrova,92 who makes out such a strong case from
her histological study in favor of the neuroglial character of the
epiphysis, seems to base her conclusions upon criteria which are
not wholly convincing, for the mere presence of demonstrable
fibers in the neighborhood of the cells does not of itself indicate
that these cells are neuroglial in character. Furthermore, this
view neglects to take into account the highly specialized char-
acter of the pineal cells. If, on the other hand, it be granted
that the cell constituency of the epiphysis is, in major part,
neurogliar, this admission would not wholly invalidate the idea
that the structure is glandular in nature, for, according to the
most recent researches of Nageotte281 and Mawas,263 neuroglia
cells contain mitochondria and hence, according to these inves-
tigators, should be considered as glandular elements. In this
light, the neuroglia throughout the entire nervous system is
endowed with secretory function. In general, however, it
does not seem necessary to invoke this interpretation of the
neuroglia in order to place the pineal body in the class of glan-
dular structures, for the character of the pineal cells is in itself
sufficient argument in favor of a function different from that

MEMOIR NO. 9

226 FREDERICK TILNEY AND LUTHER F. WARREN

attributed to neuroglia in the ordinary sense and most in favor
of a glandular activity.

The observations of Nicolas,283A later confirmed by Dimitrova,92
in which muscle cells were reported as histological elements of
the epiphysis in several Ungulates, have not been confirmed by
any other observers, and some authorities have been categorical
in their affirmation concerning the absence of such elements.
That the epiphysis may contain nerve cells and nerve fibers is
probable, but there is no evidence hi mammals of the existence
of any neural mechanism in the pineal body.

To consider the epiphysis in mammalia as a vestige in the
light of the histological evidence here summarized seems to be
an attitude which is wholly untenable, all the more so when
this histological evidence points to the fact that the structure
is a gland. For in this respect not only is the character of the
cells significant, but their arrangement in definite acini, the rich
vascular network about these acini, and the trabeculation by
means of connective tissue which gives this structure the appear-
ance common to all glands, are also suggestive of this fact.

The final conclusion to be drawn from the histological evidence
in the epiphyseal complex of vertebrates would seem clearly to
indicate that this structure of the pineal region possesses a
pluripotentiality whose fundamental, inherent tendency is in
the interest of glandular differentiation and that in a few in-
stances, as in cyclostomes, amphibia, and in primitive reptiles,
the parapineal or pineal organ may become further differentiated
in the interest of a highly specialized sensory mechanism which
has, or has had, visual function.

4. The relation of the parietal eye to the pineal body

Much of the difficulty in interpreting the relation between
the parietal eye and pineal body arises from a confusion in the
use <:f t<-nns. If by pineal body is meant the epiphysis as it
appears in mjinmials, it becomes relatively simple to discuss
Ili«' relation between Iliis structure and the third eye of verte-
brates. It may perhaps !><> arbitrary thus to limit a term which

THE PINEAL BODY 227

has not always been restricted to the sense here advocated, and
yet, as has been previously pointed out, it was from precisely
the conditions in mammals that the descriptive conception,
pineal body, took origin.

The theory that the pineal body is the vestige of the parietal
eye is accepted by many. According to this view, the third
eye of vertebrates should be regarded as primordial and the
pineal body an arrested development in the attempt to reach
such differentiation. The evidence, however, is by no means
conclusive, for, as has previously been shown, the entire epi-
physeal complex springs from a region which is fundamentally
glandiferous, while only in a very few instances is a tendency
toward sensory differentiation recognizable in it. By far the
great majority of vertebrates manifest in the epiphyseal complex
no tendency whatsoever toward the development of any neural
mechanism. This would seem to indicate that the tendency for
the epiphyseal complex to develop visual structures is a secon-
dary and not a primordial character. Furthermore, if the
pineal body was in any true sense the vestige of the parietal
eye, it would seem almost inevitable that the organ should con-
tain remnants indicative of visual specialization. The absence
of such evidence at least raises a reasonable doubt that the pineal
body had at any time possessed visual function. The almost
universal absence of true ganglionic cells as well as the lack of
nerve fibers, which may be regarded as belonging to some cate-
gory other than those of the sympathetic system, would seem to
call into question the possibility of the pineal body ever having
participated in the formation of a neural mechanism. This may
be considered negative evidence. There remains to be men-
tioned, however, the significant fact that the pineal body in all
of the higher vertebrates manifests a tendency to differentiate
along lines which cannot be interpreted as in the interests of
visual function. As has been previously shown, the differen-
tiation which does occur in the higher reptiles, birds, and mam-
mals gives rise to glandular tissue, ^rom these facts it seems
possible to conclude that the pineal body is not a vestige of the
parietal eye.

228 FREDERICK TILNEY AND LUTHER F. WARREN

The supposition advanced by Hertwig175 and others that the
pineal process in birds and mammals undergoes metamorphoses
which give rise to an organ of a glandular or follicular structure
has little to support it. Peytoureau308B maintained that in
the evolution through the vertebrate phylum the pineal body
has become partly atrophic and partly metamorphosed in such
a way as to cause a modification in the connection with the
nerve centers. Ultimately, it has taken on the characters of
an epithelial organ, in fact, a highly vascular gland represented
in the higher mammals by the pineal gland and its peduncle.
To assume that an actual process of metamorphosis, in a literal
sense, from a visual organ to a glandular structure, is respon-
sible for the differences between the parietal eye and the pineal
gland seems wholly unsatisfactory. If, however, this view has
reference to a deflection in the ontogenetic process, as a result of
which the pineal anlage in certain forms, instead of giving rise to
a visual structure, produces a gland, there may be some justifi-
cation of ascribing these changes to metamorphosis. Yet, ( ven
in this sense, to attribute the differences between the parietal
eye of Sphenodon and the pineal gland of the bird to such an
indefinite process of alteration does little more than apply a
term to the process without offering an explanation for it.

Certain investigators, among them Rabl-Riickhard,322 Ahl-
born,2 and. Spencer,368 regard the pineal body as an unpaired
parietal eye which, in many classes, for example, reptiles, appears
to be tolerably well preserved, but in most vertebrates is in a
process of degeneration. This theory goes a step further than
that which regards the pineal body as a vestige. According to
the former view, the pineal differences between such forms as
possess a parietal eye and those in which no such structure
develops are attributed to a process of degeneration, while the
latter theory ascribes them to an arrested development. Evi-
dence of degeneration in the higher vertebrates is difficult to
discern. The figures already cited in reference to the human
pineal gland (p. 158) make's it hard to believe that a retrograde
process is present, even in the late periods of life. The appear-
ance of brain sand in itself is not sufficient to justify such a con-

THE PINEAL BODY 229

elusion. Furthermore, in no instance is there the slightest
indication that the pineal body in the higher vertebrates con-
tains histological elements which may, in any sense, be regarded
as degenerated products of the visual structures in the parietal
eye. That the pineal body in birds and mammals may be inter-
preted as the result of a degenerative process affecting the
parietal eye seems wholly untenable in the absence of any con-
vincing signs of such degeneration and also because the weight
of evidence furnished by many facts indicates the glandular
nature of the organ.

It is interesting in this connection to give the opinion of
Bashford Dean,83 in which that author expresses doubt concern-
ing the connection between the epiphysis and the median eye of
vertebrates.

The evidence as to the presence primitively of a median eye in fishes
is certainly far from satisfactory. It is possible . that fishes and am-
phibia may in their extant forms have lost all definite traces of this
ancestral (visual) organ on account of some peculiar conditions of their
aquatic living. On this supposition evidence of its presence might be
sought in the pineal structures of the earliest palaeozoic fishes, whose
terrestrial kindred and probable descendants may alone have retained
the living conditions which fostered its functional survival. It is of
interest, accordingly, to find that in a number of fossil fishes the pineal
region retains an outward median opening whose shape and position
suggest that it may have contained an optic capsule. If the median
eye existed in these forms it may well have been passed along in the
line of descent through the early amphibia (where substantial traces
of a parietal foramen occur, e.g. Cricotus) to the ancestral reptiles.

The evidence that the median opening in the head-shields of ancient
fishes actually enclosed a pineal eye is now felt by the present writer
to be more than questionable. The remarkable pineal funnel of the
Devonian Dinichihys is evidently to be compared with the median
foramen of Ctenodus and Palaedophus, but this can no longer be looked
upon as having possessed an optic function, and thus practically renders
worthless all the evidence of a median eye presented by fossil fishes.

It must, for the present, be concluded accordingly that the pineal
structures of true fishes do not tend to confirm the theory that the
epiphysis of the ancestral vertebrates was connected with a median
unpaired eye. More probably it was connected with the innervation
of the sensory canals of the head.

The theory that the epiphysis in the true fishes is connected
with the innervation of the sensory canals of the head adds a

230 FREDERICK TILNKV AND LUTHER F. WARREN

new interpretation concerning the function of the pineal organ.
It is not our purpose to discuss this hypothesis, but we do desire
to emphasize the improbability of the pineal body in higher
vertebrates being the vestige of any neural mechanism. This
opinion is based on the general absence of definitely neural
elements in the pineal gland other than those connected with the
sympathetic system.

Terry3112 in Opsanus could find no evidence to support Dean's
supposition that- the epiphysis of true fishes is connected with
the innervation of the sensory canals of the head. He was,
moreover, unable to discover the evidence in the teleost to sup-
port the theory that the pineal body is an ocular organ either
degenerate or rudimentary.

The portion of the epiphyseal complex which becomes special-
ized as the eye-like structure of the lower vertebrates constitutes
the end-vesicle. This end-sac may be part of the pineal or of
the parapineal organ, depending upon the form in which it
occurs. In every instance the appearance of visual element •< is
limited to the end-vesicle. Not only is the structure notable
for the eye-like character of its histological elements, but it
occupies a position with reference to the brain and also to the
skull which further serves to distinguish it. Its connection with
the roof of the interbrain is by means of an attenuated stalk,
which gives the entire structure the appearance of a long append-
age of the brain. The junction of the stalk with the roof is
usually not a direct one since the connection in most forms is
accomplished through the proximal portion. These several
parts, which may be recognized in the pineal and parapineal
organs of certain classes, should be regarded as separate mor-
phologic entities. The proximal portion has little in common
with the end-vesicle. Its position and histological characters
mark it as strikingly different. Its only actual relation with
the vesicle is one of continuity through the stalk. This con-
tinuity may, in some cases, be almost lost or maintained only
by a small filament of nerve fibers. Such, for example, is the
condition in amphibia, a class which, perhaps, affords the most
conspicuous instance of the morphologic distinction between the

THE PINEAL BODY 231

end-vesicle and the proximal portion of the pineal organ. Were
it not for a slender fasciculus of nerve fibers these two portions
of the epiphyseal complex would appear as independent entities.
As it is, both parts are well differentiated and well developed,
one as an eye-like organ, the other with some of the characters
of a gland. This distinction between the end-vesicle and prox-
imal portion should not be underestimated. It not only shows
how remote the relationship between the two parts may be,
but also gives an added prominence to the proximal portion.
This latter part has already been shown to be the most constant
element in the epiphyseal complex, while the end-vesicle is much
more limited in its occurrence.

The process by means of which the end-vesicle and proximal
portion of the pineal organ are rendered so distinctive in amphibia
takes on a new phase in Sphenodon and lacertilia. In these
forms the necessity for the end-vesicle to assume visual char-
acters has apparently ceased, and this structure together with
the stalk is evidently in a state of involution. The contrary,
however, is true of the proximal portion which has taken on
not only more conspicuous dimensions, but also more pro-
nounced glandular characters. In the ophidians, in birds, and
in mammals the process of involution in the end-vesicle and
stalk has been carried to its final stage. No trace of the end-
vesicle or the stalk is to be found in any of the orders above
lacertilia. The proximal portion, on the other hand, in ophidi-
ans, birds, and mammals gains prominence because of its
glandular structure.

The process here described from amphibia to mammals clearly
demonstrates the progressive involution of the eye-like end-
vesicle and the gradual ascendency of the glandular proximal
portion. At one end, namely in amphibia, the end-vesicle and
proximal portion must be regarded as coordinate in prominence.
At the other end, i.e., in ophidia, the proximal portion is pre-
eminent because of the disappearance of the end-vesicle. This
phenomenon can best be interpreted on the basis of a pluri-
potentiality in the anlage of the epiphyseal complex, of such a
nature that the adaptive possibility for the development of a

232 FREDERICK TILNEY AND LUTHER F. WARREN

parietal eye or of a gland, or the simultaneous development of
both of these, is given in their origin.

According to this conception, it is not possible to consider the
parietal eye as primordial; it seems far more likely that it is an
adaptive modification developing in response to special require-
ments in a limited number of forms. The proximal portion, on
the other hand, maintains its entity with such marked per-
sistency throughout the series that it seems possessed of the more
primitive characters. This is emphasized when the proximal
portion is considered in connection with the other glandular
derivatives of the diencephalic roof. Embryologically, in those
instances in which both an eye-like end-vesicle and a glandular
proximal portion develop the anlage of these parts must have
been pluripotential. This is equally true in the instances in
which one portion of the epiphyseal complex, as, for example, the
parapineal organ, develops an eye-like structure while the
pineal organ develops a marked tendency to glandular formation.
Such an interpretation of the pluripotentiality in the epiphyseal
anlage when applied to the various orders reveals the following
conditions:

In cyclostomes the epiphyseal anlage seems to contain ele-
ments which are exclusively engaged in the differentiation of
eye-like structures which, form the pineal and parapineal eyes.

In selachians, ganoids, teleosts, and dipnoians the epiphyseal
anlage has completely lost its potentiality to differentiate as a
visual organ, and while there may be some debate as to the
character of the adult structures, there is some evidence which
points to their glandular nature.

In amphibia both potentialities are present in the pineal
organ. In Sphenodon and lacertilia both potentialities are also
present, but in these instances the parapineal portion of the
epiphytal complex gives rise to the eye-like structure while the
pineal perl ion develops glandular characters. In ophidians and
all the higlur vertebrates the potentiality for the development
< f visual struct ur< s is lost.

Kven accepting the probability of this dual potentiality, it
should be borne in mind that the median eye-like structure may

THE PINEAL BODY 233

in no instance signify a functionally active visual organ. In all
cases the attempt to develop a median eye may represent but
the abortive and partially attained differentiation of far remote
primitive ancestors in which such an eye was functionally active.
Its persistence into extant forms even as an abortive structure
may thus be taken to indicate the transmitted potentiality of
the epiphyseal complex to develop a visual organ.

The theory that the two elements in the epiphyseal complex,
namely, the pineal and parapineal organs, represent a pair of
parietal eyes similar to those of invertebrates, has little to recom-
mend it. The hypothesis of Dendy86 that the ancestral verte-
brates were possessed of such a pair of visual organs, while
interesting, is based upon too few facts in living vertebrates to
justify its acceptance. After considering the several theories
concerning the relation of the parietal eye to the pineal body, we
have come to the conclusion that none of them is adequate to
explain all of the facts. But with a full appreciation of the
investigation already devoted to this subject we desire to offer
a new interpretation which to us seems more tenable. Accord-
ing to our views, there is no direct relation between the parietal
eye and the pineal body, but each is of itself an adaptive modifi-
cation answering the demands for, or representing an inherent
impulse toward, the development of a parietal eye, on the one
hand, or of a glandular organ, on the other. In other words, the
epiphyseal anlage is pluripotential in its derivatives.

5. The phylogenetic significance of the parietal eye with reference

to vertebrates and invertebrates

Much has been written concerning the significance of the
parietal eye as one of the possible indices in the evolution from
invertebrates to vertebrates. Although little evidence bearing
upon this point has been presented in the general consideration
of this work, the subject seems of enough interest to warrant the
inclusion of the views of certain investigators who have devoted
some attention to this matter.

234 FREDERICK TILNEY AND LUTHER F. WARREN

Mathias Duval98 in 1888 brought to a conclusion a notable
series of lectures with the statement that the history of the
pineal gland has played an important role in the study of homolo-
gies in the structure of the vertebrates and invertebrates.
He further states that the situation of the pineal body in rela-
tion to the nervous system of vertebrates and in comparison
with the oesophageal ring in invertebrates gives the structure
a new significance. From this it might be possible to determine
one of the clews which should reveal how the vertebrates resulted
from the successive transformation of the invertebrates.

Several years prior to this observation, Ahlborn2 suggested
that the parietal organ was comparable to the unpaired eye of
amphioxus and tunicata, while Rabl-Riickhard322 was of the
opinion that an homology existed between the pinal organ and
the parietal eye of arthropoda. Baudouin15 expressed the view
that of the proto-vertebrates, larval ascidians possess an un-
paired eye which, however, disappears in the adult. This organ
is situated immediately beneath the epidermis and consists of
a retina, a lens, and a pigment layer. It is derived from the
cerebral vesicle and supposed to be the vestige of a transitory
eye which previously existed in adult ascidians. Indeed, in
pyrosomes this unpaired eye is well developed in the adult,
possessing a retina, lens, and optic nerve. There are no lateral
eyes in these invertebrates, and hence the unpaired eye must
functionate as a visual organ. In tunicates there exists both
the paired and unpaired eyes. In amphioxus there is a pig-
mentary patch placed above a dilation of the brain, but one
is not justified in considering this the homologue of the unpaired
eye in tunicates.

Peytoureau308* held the opinion that the pineal eye exists in
vertebrates in a degenerated state only. In extant forms of
the tunicate- it still exists as a functional organ, occupying in
Ihese animals almost exactly the same position and having the
-.•line disposition as in lizards and amphibia. In tunicates there
is an unpaired eye and two paired eyes which he believes func-
tionate simultaneously, the unpaired eye being comparable to
the parietal eye of the lixard and amphibia not only because of

THE PINEAL BODY 235

its position, but also because of its anatomy and connections.
He is of the opinion that the unpaired eye is more ancient than
the lateral eyes. This is the more probable since the ancestors
of the vertebrates were mon-ophthalmic, examples of which are
to be found in the pyrosomes which have but a single median
eye. Subsequently, the lateral eyes make their appearance in
tunicates and these functionate simultaneously with an unpaired
eye. Peytoureau308B gives six diagrams showing the degenera-
tive process from the median eye of pyrosomes to the epiphysis
in the higher mammals, as follows: 1, In pyrosomes, a simple
vesicle with a lens; 2, in larval urodela there is a vesicle with
nerve connections and nerve centers but no lens; 3, in chamaeleon
there is only an epithelial vesicle which has no connections or
neural characteristics; 4, in batrachians the oTgan is a detached
epithelial cluster having no connection with the central nervous
system; 5, in cyclodus the organ is a gland attached to the third
ventricle by means of a peduncle; 6, in mammals and birds it is
connected with the brain by a solid pedicle but presents no vesicle.
Gaskell,146 in his summary concerning the evidence of the
organs of vision and their bearing upon the origin of vertebrates,
writes as follows:

The most important discovery of recent years which gives a direct
clue to the ancestry of the vertebrates is undoubtedly the discovery
that the pineal gland is all that remains of a pair of median eyes which
must have been functional in the immediate ancestor of the vertebrate,
seeing how perfect one of them still is in Ammocoetes. The vertebrate
ancestor, then, possessed two pairs of eyes, one pair situated laterally,
the other median. In striking confirmation of the origin of the verte-
brate from Palaeostracans it is universally admitted that all the Euryp-
terids and such-like forms resembled Limulus in the possession of a
pair of median eyes, as well as a pair of lateral eyes. Moreover, the
ancient mailed fishes, the Ostracodermata, which are the earliest
fishes known, are all said to show the presence of a pair of median eyes
as well as of a pair of lateral eyes. This evidence directly suggests that
the structure of both the median and lateral vertebrate eyes ought to
be very similar to that of the median and lateral arthropod eyes. Such
is, indeed, found to be the case.

The retina of the simplest form of eye is formed from a group of
the superficial epidermal cells, and the rods or rhabdites are formed
from the cuticular covering of these cells; the optic nerve passes from
these cells to the deeper-lying brain. This kind of retina may be called

236 FREDERICK TILNEY AND LUTHER F. WARREN

a simple retina, and characterizes the eyes, both median and lateral,
of the scorpion group.

In other cases a portion of the optic ganglion remains at the sur-
face, when the brain sinks inwards, in close contiguity to the epidermal
sense-cells which form the retina; a tract of fibres connects this optic
ganglion with the under-lying bruin, and is known as the optic nerve.
Such a retina may be called a compound retina and characterizes the
lateral eyes of both crustaceans and vertebrates. Also, owing to the
method of formation of the retina by invagination, the cuticular sur-
face of the retinal sense-cells, from which the rods are formed, may be
directed towards the source of light or away from it. In the first case
the retina may be called upright, in the second inverted.

The evidence of the optic apparatus of the vertebrate points most
remarkably to the derivation of the Vertebrata from the Palseostraca.

Gaskell, in this argument, seems to have lost sight of his
\\cll-known contention that the roof of the brain in vertebrates
is to be considered the dorsal wall of the invertebrate stomach.
The stress which he laid upon this relation, to which he gave
further emphasis by calling attention to the glandular appear-
ance of the roof-plate in Ammoccetes, does not coincide well
with his idea that the pineal body is primordially a portion of a
neural mechanism. He, of course, admits that the pineal eye in
vertebrates must be considered as resulting from a neural in-
vasion of the roof-plate, yet from his contention this roof-plate
is primitively the dorsal wall of the stomach, and neural deriva-
tives appearing in it must be due to a secondary neural invasion
and, therefore, cannot be considered primordial.

In a word, by holding the pineal eye to be fundamentally
neural in structure he did injury to his own theory concerning
the evolution of the vertebrates.

Patten,303 in considering the significance of the parietal eye,
gives the following conclusions:

The parietal eye of vertebrates is homologous with the parietal eye
of such arthropods as Limulus, scorpion, spiders, phyllopods, cope-
pods, trilobites. and merosf omes, but not with the frontal stemmata
or other ocelli of iinects.

In the arthropod.-, various stages in the evolution of a cerebral eye,
are shown in detail, from functional eyes on the outer margin of the
cephalic lobes, to a median iiroup of ocelli enclosed within a tubular
outgrowth of the brain roof.

THE PINEAL BODY 237

The most primitive type of a parietal eye is seen in the nauplii of
phyllopods and entomostraca, where the eye is a pear-shaped sac, open-
ing by a median pore or tube on the outer surface of the head. In the
higher arachnids, the process of forming an embryonic eye vesicle
merged with the process of forming a cerebral vesicle, the external
opening of the forebrain vesicle and that of the parietal eye tube, form-
ing a common opening or anterior neuropore.

The parietal eye of arthropods is an important visual organ until
the lateral eyes, which represent a later product, are fully developed.
It may then diminish in size and activity, but it rarely, if ever, wholly
disappears.

During the revolution of vertebrates from arachnids, there was a
considerable period during which the lateral eyes were adjusting them-
selves to their new position inside the brain chamber, and when they
were in functional abeyance. At this period, ancestral vertebrates
were mon-oculate, that is they were dependent solely on the parietal
eye, which had come to them from their arachnid ancestors as an
efficient and completely formed organ.

When the lateral eyes again became functional, the parietal eye
began to decrease in size and effectiveness.

The parietal eye is the only one now present in tunicates. In the
oldest ostracoderms, like Pteraspis, Cyathaspis, Palaeaspis, the lateral
eyes are absent, or at least do not reach the surface of the head, the
only functional one being the parietal eye, which is of unusual size.

In the lampreys we see the same conditions, the parietal eye being
very well developed in the Iarva3, while the lateral eyes are deeply
buried in the tissues of the head, and useless. During the transfor-
mation, the lateral eyes again become functional, and the parietal
begins to atrophy, finally losing many of its structural details and its
function, although still retaining very nearly its original form.

All the theories advanced concerning the significance of the
parietal eye as an index to the process of evolution from the
invertebrates to the vertebrates have their great value in the
suggestions which they offer. To accept any of them without
further evidence seems unwise at the present time. It is pos-
sible to conceive of the median eye of invertebrates as analogous
to the parietal eye o£ vertebrates. It is, however, a long step
for the most part without the intervening support of evidence to
maintain that these structures are homologous. In fact it
seems out of the question to establish any such basis of compari-
son until this subject of homology in the invertebrate and verte-
brate brain is on much firmer ground than it is to-day. It is
evident that nothing short of the definite establishment of an

238 FREDERICK TILXKV AND LUTHER F. WARREN

invertebrate pineal region of the brain can satisfy the require-
ments in this field of homology. Not only must such an area in
its general outlines be recognized, but the demonstration must
be given that every element entering into it has its homologue
in the vertebrate brain. For this reason it seems impossible at
present to accept any other view than that the median eye in
invertebrates and the parietal eye of vertebrates are analogous.
The supposition that they are homologues, however suggestive
and stimulating, can hardly be regarded, at present, as other
than speculative morphology.

8. SUM-MARY AND CONCLUSION

I. The pineal region is preponderatingly glandiferous in its
derivatives. The morphogenetic impulse imparted by such
a gland-forming area could not fail to have a profound influence
upon one of its constituents, the epiphysis.

II. a. The pineal body cannot be a vestige from the evidence
ba.^ed upon its gross morphology, for the following reasons:

1. The phyletic constancy of the epiphysis in the vertebrate
phylum.

2. Its variations and morphologic specializations.

3. Its relatively greater phyletic constancy with reference to
other structures in the pineal region.

4. The gross evidence of its progressive specialization in
ophidians, birds, and mammals.

5. The increase in the epiphyso-cerebral index, from the
earliest stages to the latest periods of life in man.

6. The resistance to the encroachment of a prominent neo-
morph in the mammalian brain, that is, the corpus callosum,
which has produced such marked alterations in the other con-
si ituents of the dienccphalic roof-plate.

b. The pineal gland cannot be considered a vestige in the
light of the hislologieal evidence, since the tendency toward
- 1 >ecialization i- definitely in the inleresl of glandular formation
in ophidians, chelonians, birds, and mammals. Ontogenetically,
in two forms at least, in /-Y//.\ ilnnn-xlica and man, the develop-

THE PINEAL BODY 239

ment of the pineal body follows the general lines of glandular
differentiation. The pineal body is, therefore, a glandular
structure and as such, is necessary in some way to metabolism.

III. The histology of the organ gives clear evidence that the
epiphyseal complex of vertebrates possesses a pluripotentiality
whose fundamental inherent tendency is in the interest of glandu-
lar differentiation, but in a few instances, as in cyclostomes,
amphibia, and in primitive reptiles, the pineal organ may become
further differentiated in the interest of a highly specialized
sensory mechanism which has, or has had, visual function. As
a gland, it may in some cases, contribute its secretion to the
cerebrospinal fluid, but in the higher vertebrates, as in ophidians,
chelonians, birds, and mammals, it is an endocrinic organ,
contributing the products of its secretion to the blood stream.

IV. a. There is no direct relation between the parietal eye and
the pineal body, but each is of itself an adaptive modification
answering the demands for, or representing, an inherent impulse
toward the development of a parietal eye, on the one hand, or a
glandular organ, on the other.

b. The pineal body as it appears in mammals cannot be
regarded as the vestigial or metamorphosed degenerated or
atrophic residuum of the parietal eye in vertebrates.

V. The phylogenetic significance of the parietal eye in verte-
brates as the homologue of the median eye in invertebrates
should be accepted with much reservation. Until such time as
the homology between the vertebrate pineal region and some
corresponding area of the invertebrate brain is much more firmly
established than at present, the parietal eye as an index in the
evolution of the vertebrates from the invertebrates has but little
value.

The authors desire to acknowledge their great indebtedness
and to express their appreciation to Professor George S. Hunt-
ington for his assistance in the preparatine of this monograph.
They also wish to express their thanks to Professor M. Allen
Starr for his liberality in supplying the means which have made
publication possible.

240 FREDERICK TII^XKY AM) LUTHER F. WARREN

I'.IKLIOGRAPHY

•

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THE PINEAL BODY 253

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1