Pouch cows1, formerly called cow sac, received its name from the aforementioned pouch it has. It’s an interesting coincidence that its name is similar to the rhizocephala.2
On the subject of rhizocephala, it is a crustacean related to the acorn barnacle. Resembling the sac from which it got its name, at first glance it does not seem remotely related to well known crustaceans like shrimp or crabs. This change came about as an adaptation in order to parasitise other crustaceans, like the Japanese mitten crab.
As a cyprid, the female rhizocephala attaches to the body of the crab and enters the infective state. It then injects a clump of somatic cells into the crab. These cells attach themselves inside the body then pierce through the abdomen and develop its sac. The sac is an ovary, and does not have limbs or digestive organs. The cells inside the body grow root-like structures that absorb nutrients from the crab.
The infected crab becomes infertile, a phenomenon called parasitic castration.
On the other hand, cow sacs were known to be tumors in the cow’s testicle or uterus. Since they didn’t affect the cow’s health, they were believed to be benign and overlooked. But in recent years, it was discovered to be an independent organism, like rhizocephala. Moreover, it had evolved to the point where it was now part of the animal, creating a new species of cow.
The origins of the pouch cow is uncertain, but the theory that it evolved by chance is largely accepted. This is likened to one embryo of a twin absorbing the other, who becomes a tumor.
Pouch cow larvae are found in large quantities in the testicles of normal bulls. During mating season, the larvae are ejaculated along with normal sperm. They are around four centimeters in length, with no eyes or ears, two long forelimbs, a body similar to a hornworm’s, and a needle-like ovipositor.
The larvae propel themselves with their forelimbs to climb around the host cow until they find an area where the skin is thin, then inject a clump of somatic cells. As the cells grow, a new pouch develops, and the host cow becomes a pouch cow. Accomplishing this, the larvae dry up and die about two hours later.
At first glance, the larvae bear no similarities to normal cows, but can still be categorized as beings of the artiodactyla order, bovidae class. The claws of the forelimbs are split like cow hooves. This is the only remaining characteristic that show the two animals share an ancestor.
There is debate about whether a pouch cow is really inseminating the host cow, or merely robbing it of the nutrients it would usually give to an egg.
There’s a folktale, or perhaps it’s an urban legend, surrounding the pouch cow. Once, the larva was caught climbing on a cow. While it was being removed, it let out a noise that sounded just like a cow’s. The other cows heard it and became disturbed, all crying out at the same time. This author has had numerous chances to observe pouch cow larvae, but regrettably, no cries have been heard.
It’s strange how we associated the miraculous power known as cantus with the strange animal called the pouch cow, silently eating its feed.
This probably isn’t because we were managed just like these animals by our school, but because we were all burdened with an identity we were not yet aware of.
2 In Japanese, the name for rhizocephala also has the word “sac” in it.