Populations - Measuring
sex in the Asian lorises
See also determination of reproductive state
Slender lorises (L. tardigradus, L.
|Lateral vew on the
hindquarter of a L.
l. nordicus female.
The clitoris is visible; there is no prominent scrotum.
|Loris: lateral and
ventral view on
the external female genitalia.
In slender lorises, here L. l. nordicus, the genital tubercle (clitoris) of females shows a bilaterally symmetrical shape, and on the caudal side, above the vaginal cleft, a somewhat distinct-coloured central zone is visible
|Visibility of the vaginal
In red slender lorises, here probably a L. t. tardigradus or intermediate tardigradus-grandis form, the vaginal cleft may be visible (left) or during anestrus "sealed" and invisible (right). In the L. t. nordicus at Ruhr-University, an apparently sealed vagina was not observed.
|Lateral vew on the
hindquarter of L. l.
Above: with testes partly inguinal, scrotum not very prominent.
Middle: testes scrotal.
Below: testes scrotal and somewhat enlarged. The question whether this condition is related to reproductive activity is discussed; in the L. t. nordicus of Ruhr-University it seems rather related to high ambient temperature, large scrotal testes emitting more heat.
In the wild, changes from scrotal to inguinal testes were observed every night in L. l. lydekkerianus and L. l. nordicus (Nekaris 2003)
|External genitalia of a L.
Above: lateral view.
Middle: ventral view, drawn without hair, showing the areas with pigmented scrotal skin behind the penis.
Below: fully scrotal, enlarged testes (compare with left figure), lateral-caudal view, showing the pigment pattern on the scrotal skin
According to Nekaris (2003), in a wild L. t. tardigradus male caught three days after pursuit of a estrous female, the testes were scrotal, the scrotum skin was covered with a pigmented honeycomb reticulated pattern (pigmented parts raised from the surrounding skin) and exuded a pungent smelling sticky fluid, as described for pottos (Charles-Dominique) and L. t. tardigradus (Osman Hill 1953)
|Some details of the male
genitalia of L.
Above: lateral; below: ventral view. The glans penis is covered with spines; the questions whether the shape of spines may indicate taxonomic differences is still unsolved in Loris. At the tip of the glans penis, the round tip of the baculum (penis bone) is visible.
|Adult L. l. nordicus male, genital region with visible scrotal pigmentation||Subadult L. l. nordicus male, scrotal still unpigmented, testes inguinal: easily mistaken for a female||In some slender loris females, particularly in the red form L. t. tardigradus, a dark fur pattern closely resembling the pigmentation of male scrotum may be present|
Discrimination of sex in slender loris neonates
|For sexing neonates, the shape of the genital tubercle (penis, clitoris) is most helpful. In female Loris neonates (left and enlarged detail), the future vaginal cleft is hardly visible, but the clitoris shows the same bilaterally symmetical shape as in the adult female (see figures above).||Right: a newborn male. The scrotum is inconspicuous, the tip of penis resembles that of adult males (see above)|
In Nycticebus, the female clitoris is characterized by a little cranio-caudally orientated cleft in the tip, which is already well visible in neonates (H. Ribjer, pers. comm.). As in Loris, in females in addition there is also a distinct symmetrical tract on the caudal side of the clitoris
Lesser slow lorises (Nycticebus pygmaeus)
|As in Loris,
may occur because penis and clitoris are superficially
similar in size,
shape and colour.
In females, during anestrus or pregnancy, the vagina usually is sealed.
N. pygmaeus shows a breeding seasonality, and in adult males the genitalia show seasonal changes, testes increase in size during late summer. The skin of the scrotum is reticulated and seasonally becomes dark grey.
|Female external genitalia, ventral and apical view: vaginal cleft (in this figure not sealed); the tip of the clitoris is characterized by a cleft on the tip (opening of the urethra) and, as in Loris, bilateral symmetry of the clitoris||N. pygmaeus male: the shape of the pit with urethral opening on the tip of penis may be a cleft, too, but it is of more variable shape than in the female.|
|Ventral view on the external genitalia of an adult N. pygmaeus female||Adult N. pygmaeus male with scrotal testes. The scrotum has a median ridge||Subadult male with inconspicuous scrotum|
Slow lorises (Nycticebus coucang, N. bengalensis, N. (c.) javanicus)
|Female external genitalia of N. coucang: clitoris, vaginal cleft (in this figure not sealed), caudal and apical view.||Male N. coucang: penis||Different scrotal skin patterns in two Malaysian N. c. coucang from one wild population, redrawn from photos by F. Wiens|
Sources for the Asian lorises: Loris tardigradus: data from Ruhr-University and Osman Hill, 1953; animals belonging to the red subspecies obtained from Frankfurt Zoo. Nycticebus pygmaeus: drawings based on photos by Helena Fitch-Snyder, Rüdiger Lippe, Bernhard Meier, Helga Schulze and live animals in the care of R. Lippe, information partly based on the reproduction chapter in Fitch-Snyder et al., loris husbandry manual. Nycticebus coucang: drawings based on photos by Frank Wiens and Annette Zitzmann (wild N. c. coucang, Malaysia), Helena Fitch-Snyder and Karen Weisenseel.
Discrimination of sex in the African pottos
In the potto, wrong sexing may easily occur because of the presence of a female "pseudoscrotum" with a tessellated area of glandular skin which resembles the scotum and may even be larger. The organ apparently plays a role in olfactory communication (see Manley 1976).
Pottos (Perodicticus potto)
|External genitalia of a female potto with "pseudoscrotum" and glandular area superficially resembling the scrotal skin of males.||Male genital with tessellated glandular scrotal skin.|
Angwantibos (Arctocebus sp.)
|Female external genitalia of A. c. calabarensis. In Arctocebus, too, a small area of tessellated glandular skin in females was reported (Manley 1976), but it seems to be inconspicuous.||Male genital region of A. c. calabarensis with glandular area.|
Sources for African pottos: Perodicticus potto: drawings based on Osman Hill 1953, Sanderson 1940, Charles-Dominique 1966 and 1977 and Manley 1966 and 1976. Arctocebus: based on Osman Hill 1953, Sanderson 1940 and photos by Simon Bearder. .
Charles-Dominique, P., 1966: Glandes préclitoridiennes de Perodicticus potto. Biol. Gabon. 2: 355-359
Charles-Dominique, P., 1977: Ecology and Behavior of Nocturnal Primates. Prosimians of Equatorial West Africa, Duckworth, London.
Osman Hill, W. C., 1953: Primates: Comparative anatomy and taxonomy. Vol. I, Strepsirhini. Edinburgh University Press, Edinburgh.
Sanderson, I. T., 1940: The mammals of the north Cameroon forest area. Transactions of the Zoological Society of London 14: 623-725
Manley, G. H., 1966: Reproduction in lorisoid primates. Symposia of the Zoological Society of London 15: 439-509
Manley, G. H., 1976: Functions of the external genital glands of Perodicticus and Arctocebus. Pp. 313-329 in: Prosimian Behaviour, Martin, R.D.; Doyle, G. A.; Walker, A. C. (eds.), Duckworth, London.
Nekaris, K. A. I., 2003. Observations on mating, birthing and parental care in three taxa of slender loris in India and Sri Lanka (Loris tardigradus and Loris lydekkerianus). Folia Primatologica Supp. 74 (S. Gursky and K. A. I. Nekaris, eds.): 312-336.
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Lorises and pottos: species, subspecies, local populations
Last amendment: 20 April 2004
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