Question

The hexacanth larva of Taenia solium occurs in a 3 layered structure referred to as __________________
A. Proglottid
B. Oncosphere
C. Gravid proglottid
D. Cysticercus

Answer 1

Hint: Taenia solium (pork tapeworm) is a ribbon shaped, digenetic endoparasite. The adults of Taenia solium are parasites in the small intestine of human beings (Primary host) and its larva infests the muscles of pig (secondary host).

Complete answer:
The process of fertilization takes place either within the same proglottid or between two different proglottids to form zygote. The zygotes pass into the ootype, where they are enclosed by thick capsules. This capsulated zygote then passes into the uterus. Passage of capsules into the uterus is lubricated by the secretions from Mehlis's glands. The process of cleavage takes place to form a morula. The morula at the posterior end develops three pairs of chitinous hooks.

Now let us find solution from given options:
Proglottid: Strobila is made up of 800-1,000 segments of proglottids. The anterior proglottids are immature and have no reproductive organs; from about the 200th proglottids, the male organs are formed.
Oncosphere: These six hooked embryos are called hexacanth. The hexacanth is surrounded by two membranes. This hexacanth along with the membrane is known as oncosphere.
Gravid proglottid: From about 250th to 650th proglottids, there are both sex organs; these are mature proglottids. The remaining proglottids lose the sex organs and have a distended uterus filled with eggs; these are called gravid proglottids.
Cysticercus: The hexacanth then passes into the small intestine. The hexacanth is now activated by bile salts. It reaches muscles (striated) by boring through intestinal mucosa. It now forms encysted bladder worm or cysticercus larva.

Hence, the correct answer is option (B)

Note: The secondary host acquired infection by ingesting the oncospheres. The oncosphere loses its membranes by the action of gastric enzymes. The cysticercus develops in the adult tapeworm only when ingested by human beings. Pork (Pig's flesh) containing cysticerci is called measly pork for its spotted appearance; the human host gets the infection by eating undercooked measly pork. Cysticercosis is more harmful than taeniasis.