In scoliodon (Dog fish) urinary or excretory system and reproductive or genital system are firmly related to each other and together called as urinogential system. In Scoliodon sexes separate, sexual dimorphism is well marked by presence of pair of claspers in medial portion of pelvic fins.
(I) Male Urinogential System of Scoliodon:
Male urinogential system of Scoliodon consists of organs of excretory system and organs of male reproductive systems.
Organs of excretory system:
Excretory organs of male Scoliodon include a pair of kidneys, Epididymis, uriniferous tubules, ureter, urinogenital sinus and urino genital papilla.
In Scoliodon there is a pair of long, flattened ribbon like mesonephric kidneys. Both the kidneys are remaining attached to the dorsal abdominal wall, above the peritoneum, one on either side of the median line.
The kidneys extend nearly the whole length of the body cavity from the root of liver in front up to the cloaca. Each kidney is differentiated into distinct anterior and posterior parts. Anterior part is greatly reduced and posterior part is developed. Posterior part is excretory in function where as anterior part is reproductive in function.
Internal Structure of Kidneys:
Posterior functional part of kidney of Scoliodon is called Opisthoriephros (Grahan Kerr-1919). Each opisthonephros internally formed of by several coiled glandular uriniferous tubules.
Each uriniferous tubule is a coiled long narrow tube terminated by bowmen’s capsule. Bowmen’s capsule encloses a knot of capillaries called glomerulus. Uriniferous have special urea absorbing segment in them. All uriniferous tubules open into common collecting tubules. The collecting tubules communicated into common excretory tube called ureter.
This is the common excretory duct arise from the ventral surface of each kidney run along its mid ventral line in posterior direction. This is a thin walled tube formed of by union of collecting tubes emerged out of the kidney. It carries urine into urinogenital sinus.
(iii) Urinogential sinus:
This is a wide pearshaped thin walled chamber present at the n median position in between pelvic fins just behind the urino genital papilla. It opens into the cloaca. Bothe the Ureters opens into this urinogential sinus. It opening of urinogential sinus present at the tip of papilla.
Organs of genital system:
Male reproductive system of Scoliodon comprises a pair of very large elongated testes, epididymis vasa efferentia, vas deferens, and seminal vesicle, accessory organs of reproduction like claspers and siphon and hypopyle.
There is a pair of large creamish coloured tubular glands called testes attached to the mid dorsal abdominal body wall. Testes are attached to body wall by double fold membranous peritoneum called mesorchium. Posterior ends of each testes attached to calcal or gland by a non-glandular tissue.
Each testes composed of fine coiled tubules called seminiferous tubules. Seminiferous tubules internally lined by germinal epithelium which produce spermatozoa.
(ii) Vasa efferentia:
From each testis there are given off several fine tubules called vasa efferentia. These tubules run in the mesorchium to the anterior end of large Wolffian or mesonephric duct. This duct is also called as vas deferens.
Spermatozoa developed from germ cells in seminiferous tubules of the testis are carries to the vas deferens.
(iii) Vas deferens:
Vas deferens forms a very large narrow and extremely coiled duct along the entire ventral surface of the anterior genital part of kidney called epididymis.
Epididymus is the long coiled anterior part of kidney which provides a nourishing fluid for growth and maturation of spermatozoa.
(v) Seminal Vesicle:
Each vas deferens posteriorly dialated and expanded into a wide strait tube called seminal vesicle. It help in storing spermatozoa seminal vesicles of both the sides open behind separately into the urinogential sinus. It give off in front on either side an elongated clubshaped blind sac, called sperm sac.
(vi) Accessory male reproductive organs:
A pair of claspers are present on the midian portion of two pelvic fins which serve as intromittent organs in coition and copulation. Each clasper bears a closed groove with anterior opening called appyle lying near cloaca and posterior exit called hypopyle.
Spermatozoa enter apopyle from urinogential papilla of male and transferred to the cloaca of female during copulation.
Siphon is a muscular sac beneath skin of posterior ventral pelvic region. It has two channels closed anteriorly but opening posteriorly into apopyle of the grooved clasper of its side. During Copulation Sea water is drawn into siphon and forced down the clasper groove flushing spermatozoa accumulated there into the female cloaca.