Question

Onchosphore occur in
A. Ascaris
B. Faciola
C. Taenia
D. Planaria

Answer 1

It is an embryonic form of tapeworm enclosed in a spherical membrane armed with six hooks. Tapeworm belongs to phylum flatworm or platyhelminthes.

Complete Answer:
- The life cycle of taenia solium is completed in two hosts. Its primary host is man and secondary host is pig. Free larval stage is not found in them.
- Self fertilization is found in it. Fertilization occurs through copulation. During the process of copulation the cirrus segment is inserted to vagina of the same segment. The received sperms collected in seminal receptacle.
- The eggs are fertilized in the oviduct and these are surrounded by yolk and egg shells in the ootype. The capsulated eggs start to collect in the ureter because of this the size of the ureter becomes enlarged and branched and occupies the whole space. The eggs contain a large amount of yolk and each is surrounded by egg- capsule. The embryonic development starts in the ureter.
- The embryonic cell undergoes repeated cell division and the divisions are unequal so the medulla contains few larger cells, the macromeres and mesomeres forming an outer layer or inner mass of small cells.
- The micromere develops into an oncosphere. This is also called hexacanth larvae because the embryo is surrounded by two embryonic membranes with six hooks. By the process of apolysis a number of oncosphere get detached from the main parasite body and passed out through the faces.

So option c is correct.

Note: By the onchophore stage secondary host infection occurs. In the infarcted human faces the gravid proglottid containing oncosphere are present.