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Seminal receptacles of snakes.

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Department of Anatomy, Louisiana S t a t e University
School of Medicine, N e w Orleans
Successful fertilization accomplished by spermatozoa stored
within the female reproductive tract for remarkably long
periods of time (frequently referred to as “delayed fertilization”) has been reported in a number of reptiles. Listed in
table 1are the records of sperm survival f o r different species.
Considering the relatively short life of the spermatozoa of
man and most domestic animals, even the less spectacular
of the reptilian records shown here seem impressive. However, retention of sperm with fertilizing capacity has
been demonstrated for periods ranging from 5 months in
certain species of bats (Wimsatt, ’42, ’44) to nearly a year
in viviparous fish (Hartman, ’39). Extreme examples of
storage for periods of 4 to 6 years, as reported f o r turtles
and snakes, seem to be exceptional among vertebrat,es.
Despite the fact that delayed fertilization appears to be
a normal part of the reproductive pattern of many reptiles,
the location of the stored sperm has received very little attention. Most students of reptilian reproduction have assumed
that the spermatozoa remain free in the lumen of the oviduct
and that they eventually reach the infundibulum where fertilization is most likely to occur. Ludwig and Rahn (’43)
emphasized that winter storage of spermatozoa in the prairie
rattlesnake, Crotalzcs viridis viridis occurred in the lumen of
the caudal portion of the oviduct. Other histological studies of
the oviduct of reptiles (Giersberg, ’22; and Argaud, ’20) have
not suggested any structure specialized for sperm storage.
Histological examination of the oviduct of two species of
garter snakes has revealed, however, the presence of specialized glandular sacs which apparently serve as seminal receptacles.
The majority of the data upon which this paper is based
were obtained from 22 adult female Thamnophis sirtaZis Linnaeus and 23 Thamnophis elegans terrestris Fox; collected
in the vicitnity of the San Francisco Bay, California. The
oviducts were removed within three days of capture, fixed in
Bouin's solution, embedded in paraffin, sectioned at 10 p, and
stained with Mallory 's Azan.
As a background for the histological study, additional information concerning the presence or absence of sperm at a
given time of the year was obtained from microscopical
examination of smears from caudal, middle, and cephalic
regions of one of the excised oviducts of each of 130 adult
female garter snakes.
I. Histology of the oviduct
Four distinct regions can be identified in each oviduct of
the garter snake. The most caudal segment, which is nonglandular, can be designated as the vagina o r vaginal pcuch.
As in the rattlesnake, (Rahn, '42; Ludwig and Rahn, '43),
it consists of two portions. The segment which opens into the
cloaca is thick walled and bulbous. One or two centimeters
cephaled to its termination the vagina constricts abruptly to
form a straight, narrow tube several millimeters in length. The
two divisions of the vaginal pouch differ only in the thickness
of the muscular and connective tissue layers of their walls.
Both are lined by tall admixed ciliated and nonciliated columnar cells containing a pale cytoplasm and tiny, scattered,
blue-st aining granules.
Cephalad to the vagina is a long uterine segment lined by
a tall columnar epithelium consisting of intermingled ciliated
Malaclemmys centrata
(Malaclemys terrapin centrata)
Diamondback terrapin
Terrapene Carolina
Common box turtle
Yicrosaura pumila pumila
Dwarf chameleon
Solenoglyphic snakes
Pipera aspis
European asp
Causus rhombeatus
African night adder
Ancistrodon contortrix
Crotalus viridis viridis
Prairie rattlesnake
Aglyphic colubrid snakes
Tropidoclonion lineaturn
Lined snake
Coronella austriaca
European smooth snake
Thamnophis sirtalis
Common garter snake
N a t r i x natrix
Common grass snake
4 years
Barney, '22
Hildebrand, '29
4 years
Ewing, '43
6 months
Atsatt, '53
over winter
Rollinat, '46
5 months
Woodward, '33
11 days
Gloyd, '33
over winter
Rahn, '42
over winter B
Gloyd, '28
Force, '31
Rollinat, '46
over winter
over winter
3 months
over winter
Blanchard, '42
Rahn, '40
Rollinat, '46
1: years
Kopstein, '38
5 months
4 months
Kopstein, '38
Trapido, '40
44 years
Carson, '45
Natrix vittata
N a t r i x subminiata
Storeria dekayi
Brown snake, DeKay's snake
Drymarchon corais couperi
Indigo snake
Opisthoglyphie colubrid snakes
Xenodon merremi
Leimadophis viridis
Leptodeira annulata polysticta
Leptodeira albofcsca
Boiga multimacula~a
1 year
delayed fertilization ;
duration not stated.
6 years
1 year
1 year
Graber, '40
Mertens, '40
Haines, '40
Kluth, '36
Kopstein, '38
1Based on evidence of motile sperm in the female reproductive tract or on the production
of fertile eggs by isolated females.
and nonciliated cells, the cytoplasma of which usually appears
agranular. Typical uterine glands occur thickly throughout
this region, being separated by distances ranging from 20
t o 60 p. I n shape they resemble a club or flask with the
bulbous basal portion about three times as wide as the narrow
neck. Although they may best be classified as tubular glands,
actually they are intermediate between tubular and alveolar
types. Usually several glands open into the oviduct by way
of a common short duct. There is practically no lumen in the
bulbous portion of the gland and those of the ducts are very
narrow. I n hypertrophied glands, such as are found in females
during the spring, the epithelium of the bulb is composed of
large, columnar cells 7 to 10 p wide and 20 to 25 p high. The
pale-staining vacuolated cytoplasm of these cells suggests that
they are mucous secreting. The duct is formed of nonciliated,
low columnar epithelial cells (about 14 p high) which stain
similarly to or slightly darker than those of the bulb. bfacroscopically, the uterus becomes progressively more convoluted
toward the cephalic end. Histological changes in the character
of the glands also occur. The cytoplasm of the basal cells
stains more lightly and the lumina become progressively
Following the above transition region is a third distinct
division of the oviduct. This short, thick, convoluted segment
extends for 4 to 8 m m between the uterus and the terminal
infundibulum. In the garter snake this region has a histological appearance entirely different from that of the uterus
proper since it contains many highly modified alveolar glands
which appear to serve as seminal receptacles (figs. 1 and 2).
Clumps of these receptacles occur in the inner, wide connective tissue layer of the oviduct. Each alveolus is surrounded by a thin covering of collagenous fibers and groups
of alveoli are bound together by a thicker connective tissue
sheath. The larger bundles of receptacles (fig. 1) form bulges
in the oviduct wall giving it a width of over 300 p.
The receptacles appear t o be simple branched or primitive
compound glands connected to the lumen of the oviduct by
ciliated ducts. Graphic reconstruction of camera lucida
sketches indicates that frequently three to six alveoli open into
a single ciliated duct and two to five of these primary ducts
may, in turn, open into a common terminal duct.
The ducts, which occupy the oviduct wall between the more
peripherally located receptacles and the epithelial lining,
are round or oval in cross section (fig. 3) and have outer diameters ranging from 30 to 50 p and lumina ranging from 8
to 16 p. The epithelium of the ducts is conspicuous because of
its pale staining cytoplasm, deeply staining free border and
coarse, evenly spaced cilia (figs. 3 and 4). I n preparations
sectioned a t 3 p the border appears to be striated. Probably
it is similar to that of other ciliated epithelium which Fawcett
and Porter ('54) have shown to be formed of filiform processes. The cilia are coarser than those of the oviduct lumen
and unlike the latter, they form a continuous, uniform lining
(figs. 3 and 4).
The receptacles are composed of a single layer of palestaining, agranular, nonciliated cells. I n many empty receptacles the cytoplasm is interrupted by large apical vacuoles.
I n some receptacles with sperm the vacuoles appear to have
been penetrated by the sperm. The size and shape of the
epithelial cells vary considerably. I n empty receptacles the
cells are usually roughly cuboidal and range from 10 to 22 CI
in width or height (figs. 3 and 4). Receptacles containing
dense sperm bundles have a much thinner epithelium. Although this frequently reaches a height of 10 p it is more often
only 1to 5 p tall (fig. 2). The cytoplasm is thinnest where the
sperm heads press against it, and in some instances it is not
clearly discernible through the optical microscope. The cavities of the individual alveoli range from 10 to 20 p when empty
of sperm. When filled with sperm they may be enlarged to
20 to 5 0 ~ .The outer diameters of the alveoli range from
25 to 80 p whether filled with sperm or empty.
I n sections with a thickness of 10 p counts of spermatozoa in
individual receptacles ranged from one to several hundred.
The distribution of sperm throughout the oviduct as observed
in serial sections indicates that as the sperm move cephalad in
the lumen they tend to fill the receptacles as they encounter
them. The most cephalic receptacles are usually empty.
Occasionally sperm have been observed in the mouth of the
ciliated ducts. A lack of orientation in reference to the duct
suggests that they were being swept in broadside rather than
entering by their own locomotion. However, the possibility
of distortion due to fixation can not be ignored.
I n contrast with the entangled masses found in the lumen
of the oviducts, the larger bundles of sperm in the receptacles
have an orderly arrangement, with closely packed sperm heads
oriented against the alveolar epithelium and the bundles of
parallel tails filling the lumen in undulant waves (figs. 1 and
The seminal receptacles are not uniformly distributed, but
tend to occur in groups which are most frequently found a t
the corners of the folds in the oviduct (fig. 5). The deeper
crypts of the folds receive most of the ciliated tubules and
are partially lined with the same type of dense, coarse cilia.
Between these clumps the more thinly ciliated epithelium is
raised into narrow folds such as are characteristic of the
I n the latter segment the plicae of ciliated epithelium become
higher whereas the connective tissue and muscular layers
become thinner. Groups of mucous-like cells occur frequently
at the bottom of the crypts between certain of the folds. Other
glandular cells are absent. As the infundibulum flares out
toward the ostium the entire wall becomes much thinner, and
the plicae and epithelial cells gradually decrease in height.
11. Seasonal distribzctioN of sperm in the oviduct
A survey of the seasonal distribution of sperm in the female
reproductive tract was undertaken to determine whether the
seminal receptacles are utilized f o r the storage of sperm
during the winter following fall copulation, and if they are
capable of storing sperm for even longer periods of time.
Field observations revealed that one of the species studied,
Tharnnophis sirtalis, mated in the fall as well as the spring.
I n the three year period of study over two thousand garter
snakes were collected. Fall copulations were observed in T.
sirtalis twice but were never observed in T . elegarzs. Smears
taken from the caudal and cephalic ends of the oviduct
revealed the onset of the mating periods in the two specks and
corroborated the field observations.
No sperm were found in smears from any of the 23 adult
post-partum female T. sirtalis collected from the beginning of
August through September. Only 4 out of 14 specimens of this
species captured in October were inseminated. I n these animals the sperm were limited t o the caudal half of the oviduct.
Sperm were also found in the caudal o r middle regions of
the oviduct of certain females killed in November ( 2 out of
5), December (1out of a ) , and January (2 out of 3). The single
February specimen contained sperm throughout the uterus
and vagina. Smears of 6 T . sirtalis collected in March revealed
that 4 had sperm in the cephalic end of the oviduct; the other
two had not yet been inseminated. Three out of 4 specimens
collected in April had sperm in the uterus ; in two of these the
sperm had reached the region of the receptacles. Five females of the May sample had large yellow ovarian follicles and
sperm in the cephalic half of the oviduct. Also present in
this sample were three adult females with negative sperm
smears. The ovaries of these animals contained small corpora
lutea, indicative of a previous pregnancy, and small white
immature follicles, but no ripening follicles. Undoubtedly
these individuals would not have had young that year. Most
female 2'. sirtnlis ovulated during May. All were inseminated
prior to ovulation. A few sperm were found to survive in the
caudal oviduct of gravid females through early August.
No sperm were found in smears obtained from over 50
adult female T.e. terrestris captured from the beginning of
August through November. Smears of this species during the
spring revealed that sperm were present in the caudal end
of the oviduct in a few specimens by the end of March.
During April and May they were found a t various levels of the
tube. Ovulation in this species occurred during the latter
half of May and the early part of June. All females examined
just prior to ovulation were inseminated. Sperm persisted in
the caudal end of the oviduct in gravid females through July.
Data regarding the presence or absence of sperm in the
receptacles were obtained from a representative series of
histological preparations. The receptacles of 11 T. sirtalis
sacrificed during the period extending from the end of July
through January contained no spermatozoa, indicating that
sperm had not survived the summer gestational period. Two
of the five specimens killed in December and January contained sperm in the caudal two-thirds of the oviduct from a
fall insemination, but the sperm had not yet reached the area
of the receptacles.
The single February specimen of this species had a few
sperm in the receptacles. I n the March sample 5 of the 8
females sectioned possessed sperm in the receptacles. I n most
of these snakes the sperm had only reached the level of the
most caudal receptacles. The receptacles of the two April
specimens contained large bundles of sperm.
No sperm were found either in the lumina or. in the receptacles of the sectioned oviducts of 15 adult female 2'. e.
terrestris sacrificed between July and January. Further, seetions through the oviducts of 4 specimens of this species
collected in March revealed no sperm in the receptacles. By
April sperm had entered the receptacles in three of the four
snakes sectioned.
Nearly all snakes with large numbers of compact bundles
of sperm in the receptacles also had large masses of disorganized sperm distributed throughout the oviduct lumen,
suggesting a relatively recent insemination. However, among
the spring material were two very significant specimens that
contained variable numbers of sperm in the receptacles but
did not have a typical distribution of sperm in the oviduct
One large female T . e. terrestris, collected April 29th, was
found to have many well filled receptacles and several entangled masses of sperm in the lumen. The latter were located
only at the openings of a few of the ciliated ducts. The distortion of the adjacent receptacles strongly suggested that
these sperm had been forced out when a smear had been taken.
Over 400 sections which sampled the entire right oviduct of
this specimen were thoroughly examined and no other sperm
were found. Smears revealed no sperm in either the uterus or
vagina of the left oviduct.
The second specimen, a female T . sivtalis, was captured
April 8th. I n this animal a few receptacles contained large
masses of sperm but neither sections nor smears revealed
sperm in either the adjacent or caudal regions of the oviduct
Most students of reptilian reproduction, adopting the terminology suggested by Giersberg ( ’22), have distinguished
three major regions in the oviduct of lizards and snakes: (1)
a short caudally located vagina, (2) a long middle segment
termed the uterus, and (3) a cephalic portion designated as
the tube and infundibulum. The above reptilian groups apparently lack the specialized albumen secreting portion which
in birds and turtles lies between the uterus and tube. There
has appeared in the literature, however, a misuse of the term
“tube.” In their study of the prairie rattlesnake, Ludwig
and Rahn (’43) incorrectly applied this term to the thick
convoluted portion situated between the infundibulum and the
uterus. A careful review of Giersberg’s ( ’22) descriptions of
the tube in birds, turtles, lizards and snakes indicates that
he regarded the tube as the transitional, tapering, funnel
shaped portion connecting the infundibulum or fimbriated
opening to the thicker uterus. His descriptions of the snake
and lizard oviduct make no reference to a particularly specialized glandular area anterior to the uterus. I n the garter
snake that segment of the oviduct which Ludwig and Rahn
(’43) designated as the tube differs histologically from both
the uterus and infundibulum. Since the modified glands that
characterize this region were found to be well filled with sperm
in all female snakes killed just prior to ovulation, there can
be no question but that these structures serve as at least
temporary sperm receptacles. Both in position and structure
they are admirably suited for this function.
Their location at the cephalic end of the oviduct places a
reservoir of sperm in a position favorable for fertilizing the
eggs very shortly after the latter enter the oviduct. Whereas
free sperm in the lumen could easily be swept caudally by
the eggs passing towards the uterus proper, those in the
receptacles are protected. Further, as the passing eggs stretch
the oviduct wall and exert pressure on the receptacles, sperm
would be forced out into the lumen at the time when they are
most needed for fertilization. It seems logical to propose that
each egg would force out a certain proportion of the stored
sperm and the supply would gradually be depleted. Such a
mechanism could explain the incomplete fertility within
batches of eggs such as has been reported f o r the indigo snake
(Carson, '45).
The presence of coarse cilia in the ducts, an unusual specialization f o r exocrine glands, suggests that the cilia may be
instrumental in aiding the sperm to reach the receptacles.
Although, as previously noted, certain aspects of the histological preparations encourage the notion that the spermatozoa are swept into the receptacles by the cilia, it is also
possible that the latter create currents directed toward the
oviduct lumen and the sperm swim against these currents to
find their way into the alveoli. The latter suggestion might
better explain the precise parallel organization of the sperm
bundles within the receptacles.
Not only do the receptacles offer a physical refuge for the
sperm, but theoretically at least, they could be of physiological
importance to their nutrition or chemical arrest of activity.
The frequent occurrence of compact bundles of neatly arranged sperm is in keeping with the concept that concentrated
masses of sperm tend to display reduced activity with a
consequent conservation of energy. Further, histological
preparations demonstrate that where sperm are present in
the glandular receptacles the epithelium is thinner, the cavities are enlarged and the apical vacuoles are invaded. Since
the dimensions of the connective tissue sheaths which surround the clumps of receptacles do not vary with the presence
or absence of sperm, there is no evidence that the stored sperm
swell the alveoli and consequently stretch the epithelium to
a thin sheet. Rather, it appears that the cytoplasm diminishes
in the presence of the sperm, especially where it is in contact
with the sperm heads. Whether the response of the cytoplasm
merely represents another example of the lytic activity of the
sperm heads or whether the sperm receive nourishment during
this process is, at present, a matter for speculation.
The only other description of a similar sperm storing
mechanism in vertebrates of which the author is aware is
that by Van Drimmelen ( ’46) for the domestic fowl. He
observed “spermnests” in the caudal half of the chalaziferous
region of the hen oviduct which were composed of bundles
of 50 to 80 parallel spermatozoa with their heads in a nonciliated fundus and their tails extending into a ciliated duct.
In location and morphology these “spermnests” bear a resemblance to the seminal receptacles of the garter snake. However, it is impossible to judge from his photographs and brief
descriptions whether the structures found in the hen and
the garter snake are homologous.
Despite the apparent suitability of the receptacles f o r
sperm storage, the data do not support the hypothesis that
these structures are utilized for the overwintering of sperm
following a fall copulation. Although field observations and
sperm smears have demonstrated that the west coast populations of 2‘. sirtalis involved in the present study resemble
eastern populations of this species (Blanchard and Blanchard,
’41) in having a fall as well as a spring copulation, sperm were
not found in the receptacles of representatives of this species
until February or March. This was only slightly earlier than
they appeared in the exclusively spring breeding species, T.e.
terrestris, in which sperm were first seen in the receptacles
in April. It is difficult to see why sperm were found only in
the caudal two-thirds of the oviduct of T.sirtalk killed from
October through January and why they did not migrate
cephalad into the receptacles as they did in both species just
prior to ovulation. Puzzling as these data are, they agree with
the findings of Ludwig and Rahn ( '43) for the prairie rattlesnake. I n the rattlesnake, sperm deposited in fall copulations
are retained in the caudal end of the oviduct through January.
The above authors suggested that coils in the oviduct prevented the cephalad migration of the spermatozoa. No mechanical blocking of this type was observed in the garter
There is little evidence that having once reached the receptacles prior to ovulation, the sperm are stored past the time of
parturition. Although Rahn ( '40) found viable sperm in fresh
oviducal smears from gravid female T.sirtalis during July
and August, Blanchard and Blanchard ( '41) presented evidence that sperm do not survive beyond parturition in this
species. While I have not sectioned the oviducts of gravid
females, data obtained from smears indicate that in both T.
sirtalis and T. e. terrestris sperm are not present in the
cephalic end of the oviduct of specimens killed subsequent to
late July, although gravid females may have a few sperm in
the caudal end of the uterus and vagina as late as July or
early August. Aside from the two possible exceptions discussed below, all post-partum females examined by smears or
sections completely lacked sperm.
The unique April T. e l e g m s which contained abundant
sperm in the receptacles but none throughout the lower oviduct
does not conform to the picture presented by other recently
inseminated snakes. One must either assume that there was
a rapid and complete migration into the receptacles or, since
this species does not mate in the fall, a retention of sperm
from the previous spring insemination. I n either case, the
specimen would be unique, but it should be emphasized that
it was one of the most completely sectioned and examined
specimens in the entire series.
The second aberrant example, an early April T. sirtalis,
showed no evidence of recent insemination. She had fewer
sperm in her receptacles than are commonly present in snakes
prior to ovulation. This, plus the absence of sperm in the
oviduct to testify to either a fall or an early spring insemination, indicates storage f o r at least one year. These two
specimens suggest that although in garter snakes sperm
usually disappear by the end of parturition, they may occasionally survive in the receptacles for as long as one year.
Neither of the species studied has been demonstrated to
have extremely long records of sperm storage comparable to
those reported f o r the indigo snake or the tropical night snake.
Although absolute proof that the receptacles described in this
paper are responsible for prolonged sperm storage is still
wanting, the data indicate that these sacs are the most
suitable structures in the snake oviduct for housing sperm.
I should like to thank. Drs. C. M. Goss and M. H. Fox for
their criticism of the manuscript and Dr. G. W. D. Hamlett
for his suggestions regarding the interpretation of the histological material. The photomicrographs were prepared by the
Department of Medical Illustration, Louisiana State University School of Medicine.
1. The lumina of modified glands at the base of the infundibulum of the oviduct of female garter snakes are frequently
found to be filled with sperm arranged in compact, orderly
bundles. This is particularly true of specimens killed just prior
to ovulation.
2. The epithelium of the specialized alveolar glands .is pale
staining and much reduced in height where in contact with
the sperm heads. The alveoli open into the lumen of the
oviduct by means of branched, heavily ciliated ducts.
3. Both in position and morphology the glandular sacs
appear specialized to serve as seminal receptacles.
4. Unlike Thawmophis elegam terrestris, Tharnwophis sirtulis frequently mates in the fall. Sperm deposited by a fall
mating spend most of the winter in the caudal two-thirds of
the oviduct and do not enter the seminal receptacles until
February or March. I n the spring mating form T. e. terrestris,
sperm appear in the receptacles in April.
5. Although sperm do not usually survive in the receptacles
beyond parturition, the data suggest that in two females sperm
were retained from one spring breeding season to the next.
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the prairie rattlesnake. Copeia, 1943 : 15-18.
R. 1940 Neuere Beobachtungen uber die Fortpflanzung der Schlangen.
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of the bat. Anat. Rec., 83: 299-306.
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reproductive tract of the bat. Anat. Rec., 88: 193-204.
S. F. 1933 A few notes on the persistence of active spermatozoa i n
the African night adder, Caz~susThornbeatus. Proc. Zool. SOC.London.,
1933: 189-190.
1 Wall of the oviduct showiiig receptacles filled with sperm. The alveoli are
surrounded by dark staining connective tissue sheaths. x 255.
2 The seminal receptacles packed with spermatozoa. Note the compact, parallel
arrangement of the sperm and the reduced epithelium of the alveoli. x 1000.
and 4 Region of seminal receptacles showing (a) ciliated ducts with dark
staining border leading to ( b ) nonciliated alveoli. The epithelium of these
empty alveoli is tall. x 666.
Low power view of longitudinal section extending through 8 mm of the convoluted cephalic end of the oviduct showing region of seminal receptacles between
the uterus and the infundibulum. The seminal receptacles (a) can be recognized by their empty lumina; the uterus is characterized by darker staining
glands ( b ) ; epithelial plicae (c) begin in the region of the seminal receptacles
but are more highly developed i n the infundibulum, a segment of which
appears a t the upper left of the photograph. X 22.
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seminar, receptacles, snakes
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