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MALE REPRODUCTIVE DUCTS AND GLANDS

   In gnathostomes (jawed vertebrates) , part of the mesonephros from the urinary system is used to transport sperm and sperm are no longer released into coelom (Romer, p. 409).  In sharks and amphibians, male reproductive ducts known as efferent ducts travel from the testes to the kidney.  The situation in bony fish is variable but connections between the testis and kidney are absent.  In some fish, the archineprhic duct transports sperm, becoming a ductus deferens and, on becoming highly coiled, an epididymis.  Seminal vesicles and sperm sacs may also develop in fish (Weichert, 1970).  Amphibians possess a ductus deferens and an epididymis (Weichert, p. 319).  In many mammals, an enlargement of the vas deferens, the ampulla, may store sperm. (Weichert).

 

GLANDS

    Mammalian semen not only contains sperm, it contains secretions from accessory sex glands.  Sperm never travel through these glands but their secretions facilitate reproduction.  Mullerian glands exist in amphibians which are thought to be the homolog of the prostate (Sever, 1991).   No accessory sex glands are known in male turtles (Weichert).  In monotremes and marsupials, bulbourethral glands are the only accessory gland. Marsupials may possess 1-3 pairs of bulbourethral glands.  Although marsupials lack a prostate gland per se, they do possess prostate tissue which is diffusely organized into numerous small glands, internal to the urethral coat.  Definitive prostate glands and seminal vesicles are structures known only in placental mammals (Weichert; Stonehouse, 1977)

SHARK

SHARK

SHARK
SHARK

FROG

FROG

CATCAT CAT
CAT
SHEEPSHEEP

MONKEY

MONKEY

MONKEY
MONKEY MONKEY
MONKEY MONKEY

SCROTUM 

    In most placental mammals, the cloaca is lost except for ventral portion which is retained in females as the vestibule (Romer, p. 439) and the testes descend into scrotum (Romer, p. 441).   As mammals evolved a higher metabolism, there existed the danger of infertility due to the effect of higher temperatures on sperm.  In all mammals, the male (and female) gonads and ducts develop near the kidneys, as in the ancestral condition.  In females, the ovaries then descend to the pelvic brim.  In males, the testes and their ducts descend outside the body cavity into the scrotum where the temperature is a few degrees lower.  In males, the vas deferens travels from the testis, through the inguinal canal, around the bladder to the seminal vesicles and the prostate.  Although this does allow males to be fertile with a higher body temperature, it leaves them vulnerable to inguinal hernias.

     In monotremes, the testes don’t descend at all while in all other mammals they descend at least as far as the pelvis (Weichert, p. 310).  Testes are located in the abdomen in some mammals such as the marsupial Notoryctes (Stonehouse, 1977), insectivores, most edentates, whales, elephants, hyraxes, sirens, rhinos, and many seals.  Periodic descent of the testes occurs in some insectivores and bats, most rodents, and in wombats, otters, and lamas.  The testes are located permanently in scrotum in virtually all marsupials, some insectivores, primates, some edentates, most carnivores, some seals, most perissodactyls and artiodactyls.  In marsupsials, the scrotum is located anterior to the penis, unlike its position in placental mammals (Weichert, p. 310-3).  Unlike the condition in many primates, the scrotum of chimpanzees and humans is located postpenially (Gibbs, 2002).

  

PENIS

    In most fish and amphibians, fertilization of the ova occurs outside the female’s body.  Some fish and amphibians reproduce through internal fertilization and some part of the male anatomy has been modified to introduce sperm into the female’s body, often the cloacal lips.  All amniotes reproduce through internal fertilization and the male ancestors of modern amniotes evolved a penis with an erectile corpora cavernosa and a terminal glans penis to serve as the intromittent male organ (Romer, p. 441).  In birds, the penis exists in ducks, geese, swans, and ostriches where it is similar to that of  crocodiles.  In many other birds, a rudimentary penis is present  (Weichert, p. 327).

     The penis of monotremes is similar to that of turtles and crocodiles in that it is located within the cloaca.  The monotreme penis possesses a glans and a foreskin. (Weichert, p. 327; Romer, p. 441).  The penis is bifid in most marsupials, thus directing sperm to the lateral vaginas (Stonehouse, 1977).  Some marsupials have the unusual feature of an everted penis.  This structure is present in Antechinus apicalis although a second member of the genus, A. stuartii,  lacks it.  It is present in 43 of 54 species of Dasyuridae (Stonehouse, 1977).

MONKEY

MONKEY

MONKEY
HUMAN MODEL

HUMAN MODEL

HUMAN MODEL

HUMAN MODEL HUMAN MODEL
The following illustration represents the male reproductive structures of the chimpanzee.
CHIMPANZEE