Enkishi Mating and Reproduction Infodump
So here's an old block of info about the Enkishi species specifically, detailing a bit of their anatomy and how they reproduce.
The Enkishi
The enkishi are first among the Sacred caste, and the most advanced civilization within the Goddess Enillishi's realm. They are at about a bronze age level and have a rudimentary knowledge of basic metallurgy, complex forms of plumbing, and advanced stonemasonry. Being of a Sacred caste, they share a symbiotic relationship with an aquatic species which dwells within the rivers and reservoirs near their settlements in order to successfully reproduce. As such, their culture has particular nuances regarding mating habits and rearing of offspring.
They generally possess long bodies, standing a little over 6 feet (2 meters) tall when hunched forward in their natural posture. From snout to tail tip they are approximately 6 meters long, the tail being twice the length of the spine. Their skin is smooth and colored a pale grey, tinted dull blue. The blue pigmentation is darker along their back, flank, and top of their head.
They are semi-aquatic but do not possess any amphibious ability once they come of adolescent age. Though they tend to be natural swimmers, only the first three months are spent in an aquatic larval stage, the newly hatched offspring resembling small eel-like creatures about 4-5 inches (10-13cm) long. During this time, offspring are generally unaccounted for, as not all larvae are expected to survive. They grow rapidly during this period, growing limbs and lungs and eventually crawl out of the water. The offspring then enters its adolescent stage, and is cared for by adults.
Some cultures maintain enclosed spawning pools for each couple's offspring, while others mix them all together, choosing which young to raise by a method other than direct hereditary lineage. Though the offspring are rather self sufficient in their larval stage, they grow to become quite helpless once they leave the water, and must develop more refined motor skills to use their new limbs. The newly emerged infants resemble miniature versions of the adults in physical appearance. Mental development takes place during this stage as well. Enkishi become sexually active after roughly 13 years, at which point they are encouraged to choose a mate. However, some cultures may encourage males to become students in a trade instead, discouraging actual mating until a later age, as often a male that sires offspring is expected to then become a brood male.
Mating and Reproduction
The enkishi reproductive cycle relies on a mutual symbiosis with the 2nd caste of Sacred, these being large, aquatic, serpentine creatures called the Illiyel, which while not civilized in a technological way, are still sapient beings. As such, the enkishi female is equipped to take advantage of this relationship, in order to nurture their offspring to maturity. This has effectively eliminated the need for the development of either the amniotic egg, or the placenta. The creature implants a womb into the male enkishi's bladder along with its own eggs, which develop and hatch within, causing the male to birth them. The enkishi female also lays her eggs into this surrogate womb, the eggs being compatible with the parasitic, uterine tissue.
Females ovulate bimonthly, the eggs taking a week or two to develop and migrate from the ovaries into the ovichamber. During this time the female experiences an increase in libido. Once developed, the eggs are nurtured by the surrounding tissue within her ovichamber, and await fertilization. Fully developed eggs are a translucent, dark red and no larger than the size of a pea (1cm). She can produce anywhere between 6 and 20 during a single ovulation. Once fully developed, her libido increases steadily, as her ovichamber and surrounding sexual glands produce and accumulate maternal fluids, eventually pushing her abdomen out and giving her a gravid appearance. If no suitable male can be found for her to lay in, she may discharge her eggs and fluid via a kind of masturbation.
Typically, the male will copulate with the female, using his penis to fertilize her eggs internally, usually after her ovulation but before the accumulation of fluids. After fertilization, the male would undergo the symbiosis, finding a gravid, female illiyel and allowing her to implant her womb into his bladder, along with her eggs. While the male carries the illiyel's offspring and nurtures them, the enkishi female's eggs develop further, forming embryos. The eggs grow a little larger, approximately 12mm in diameter. The inner tissue of the ovichamber is not able to support the growth of the embryos, and so the offspring cannot develop further until they are deposited within the illiyel's surrogate womb.
The illiyel's offspring develop within approximately 6 weeks. The eggs dissolve around the embryos as they grow, forming amniotic sacs. The offspring emerge from these, leaving their pseudo-placentas embedded within the uterine wall to be reabsorbed, and are birthed through the male's urethra. For this purpose, the enkishi male's urethra is wide and elastic, reducing ejaculation force in favor of allowing the birthing process to be less risky. After birthing, the enkishi female would be fully gravid and ready to lay. Using her ovipositor, she penetrates the male's urethra all the way to the surrogate womb, and lays her eggs, as well as inflating it with her volume of fluids. The process involves an intense orgasm for the female, and the extensive stretching of the male's bladder is usually painful for the male. As a result, most males tend to try and avoid becoming brood males for the gravid females, leading to gravid females becoming more sexually aggressive, often pinning reluctant, prepared males down and forcing them to carry their eggs. This behavior is typically shunned however, and the aggressiveness of gravid females is often vented in other ways.
The enkishi eggs take longer to develop, taking over two months for the embryos to further develop. The eggs dissolve into sacs, just like the offspring of the illiyel, however, the embryos do not develop a placenta. Instead, nutrients and waste are exchanged through the thick uterine tissue in which they are embedded via diffusion. The fully developed young resemble serpentine tadpoles. They are birthed in the same manner as the illiyel offspring, and live in the water for another three months as they grow larger and develop limbs and lungs. When they emerge from the water, enkishi infants are about 16 inches (40cm) long in body size, not including the tail and are unable to walk bipedally.