The spermatheca is the sperm storage organs of the female reproductive tract in bees, ants, cockroaches, some molluscs, oligochaetes like earthworms, and certain other invertebrates and vertebrates like frogs. It is ectodermal in origin as outgrowths of the median oviduct generally originate near or on the genital chamber and produce a cuticle lining. It stores maintain and releases sperms at the appropriate time during fertilisation. It provides nourishment, long-term storage, and viability for sperm. It also protects sperm from mechanical damage, contact with the hemolymph, and putatively from free radicals.
Spermatheca in Organisms
The spermatheca (multiple storage organ) is also called receptaculum seminis. It helps the female segregate and manipulate the sperm. It differs considerably in their size and overall structure between insects. It generally originates from the median oviduct near or on the genital chamber and produces a cuticular lining. As outgrowths of the median oviduct, they are all ectodermal in origin.
In Cockroaches
In cockroaches, a pair of spermatheca is present in the 6th segment, opening into the genital chamber. The larger spermathecal sacs store spermatozoa received from the male during copulation. In the gland, separate secretory units are associated with epithelial duct cells that receive secreted materials and transport them through the reproductive tract’s tissue.
In Earthworms
An earthworm is a hermaphrodite animal that exhibits cross-fertilisation. It has a flask-shaped spermatheca. Spermathecae are pouch-like structures, also called seminal receptacles, storing the sperms received from the other worm during copulation. They have variable shapes and are lined with epithelial tissue. The spermatheca opens externally by small ducts. Four sets of spermathecae are situated in the sixth-ninth sections (one set in each portion). They get and store spermatozoa during copulation.
In Frogs
Sperm storage is observed in most species of salamanders and one species of frog, but it is unknown in caecilians. In contrast to oviductal storage, sperm are stored in cloacal glands called the spermatheca.
Spermathecal Structure
The spermathecal sacs (receptaculum seminis) have a secretory duct (ductus seminalis) through which they discharge their contents into the genital chamber. The capsule may also contain specialised secretory cells that produce substances that support the viability and activation of the sperm. Within the spermathecal sac, sperm move quite actively, and secretions of the secretory cells provide nourishment, long-term storage, and viability for sperm.
Spermatheca’s primary functional parts generally include the spermathecal duct, reservoir, muscular pump, and spermathecal gland. After copulation, the sperm migrate from the genital chamber of the female reproductive tract to the spermathecal duct and then to the reservoir.
When the eggs have been released from the ovary, the sperm retrace their route, and fertilisation occurs. The female genital tract, including the spermatheca, is involved in the maturation and activation of sperm. Within the spermatheca, sperms are protected from mechanical damage, contact with the hemolymph, and putatively from free radicals, like reactive oxygen species such as superoxides. Antioxidative enzymes in the spermatheca may protect the sperm from oxidative damage.
Number of Spermatheca
A female insect typically has one spermatheca, but some coleopterans have two. There are three spermathecae in some dipterans.
The Spermathecal Reservoir
The reservoir cuticle is crucial for keeping the gametes isolated from the external environment and from components of the hemolymph that could cause damage to the sperm. Functionally, however, the reservoir’s role is always allocating and maintaining sperm. The reservoir is spherical in most insects. It has been suggested that the spherical reservoir provides sperm for fertilisation, while the tubular reservoir secondarily stores and provides gametes for egg fertilisation.
Spermathecal Duct
The spermathecal duct connects the reservoir with the proximal portion of the female reproductive tract, allowing the transit of sperm in both directions.
Spermathecal Gland
The spermathecal gland secretions probably play a role in maintaining sperm viability. Glycogen, glycoproteins, and phospholipids are found in the gland secretions that promote sperm nutrition in the spermatheca. Gland secretions also contain glycoproteins, and mucopolysaccharides increase the motility of sperm.
Conclusion
Spermathecal sacs are sperm-storage organs of the female reproductive tract in insects, some molluscs, oligochaetes like earthworms, and certain invertebrates and vertebrates. It is ectodermal in origin as outgrowths of the median oviduct generally originate near or on the genital chamber and produces a cuticle lining. It stores maintain and releases sperms at the appropriate time during fertilisation.
The earthworm has one pair of spermatheca in each segment from the 6th to the 9th segment. It stores and nurtures sperm that earthworms receive from their mates during copulation. In female cockroaches, a pair of spermatheca in the 6th segment opens into the genital chamber. The larger spermathecal stores spermatozoa received from the male during copulation.