Introduction to the Cestodes
Adult Bodyplan
Cestode Tegument
Larval Metacercaria
Reproductive System
Infections of Man
Specific Cestodes
The Reproductive System of The Cestodes
The cestodes are all hermaphroditic organisms. Moreover, as previously described, each individual proglotid contains a complete set of reproductive organs, although these develop at different rates, with the male organs usually developing first. The female system consists of an ovary, vitelline (yolk) glands, a Mehlis gland that surrounds an Oötype. These organs together form the egg, which then passes into the uterus on fertilisation as sperm pass down through the parasites vagina. The male reproductive organs consist of a number of testes conected by sperm ducts (vas deferens), the end of which is modified to form a muscular cirrus, which is retractile into a genital atrium (into which the vagina also opens). Self fertilisation within a single segment may occur, but this is usually prevented by the differential maturation of the sexual organs. More commonly either different segments fertisile each other, or if more than one parasite is present, cross fertilisation may occur. The precise organisation of the parasites sexual organs may be used to distinguish different groups of these parasites. These parasitology pages concentrate on the two groups of cestode that infect man and domesticated animals, the Pseudophyllideans and Cyclophyllideans. These have highy distinctive proglotids, as described below.
The Pseudophyllidean Proglottid
Proglotid of D. latum
The Female Reproductive System |
The Male Reproductive System |
| Ov - Ovary (bilobed in D. latum.) Oo - Oötype (where the egg is formed) Ut - Uterus (In the pseudophyllideans this opens to the outside, via the uterine pore) Ut p. - Uterine pore (not present in the cyclophyllideans) V - Vagina (a long straight tube) Vt - Vitelline glands (secreting substances that go to make up the egg yolk and shell) Vt d. - The Vitelline duct (connecting the vitelline gland, which are diffuse and are situated lateraly in D. latum. M - The Mehlis gland (A cluster of unicellular shell glands, absent in some species) |
T - Testes (dorso-lateral in D. latum. V - Vas deferens C - Cirrus (a protrusible muscular organ, opening anterior to the vagina in a common genital atrium)
L E C - The Lateral Excretory Canal |
The most important difference between the proglottids of Pseudophyllidean tapeworms and those belonging to the Cyclophyllideans is that in the Pseudophyllideans the uterus open to a pore. In consequence fertilised eggs are shed continuously from the proglottids, rather than accumulating in the uterus as is the case with the Cyclophyllideans. In general structure the reproductive system of tapeworms of this group is very similar to that of the Trematodes as are the shells of the eggs produced by these parasites (i.e. eggs are thin walled with an operculum).
The Cyclophyllidean Proglottid
Proglotid of Taenia sp.
| Ov - Ovary (bilobed in D latum.) Oo - Oötype (where the egg is formed) Ut - Uterus (In the cyclophyllideans this fails to establish a uterine pore) V - Vagina (a long straight tube, sometimes with a seminal receptacle) S - Seminal receptacle (an enlarged chamber, used for the storage of sperm) Vt - Vitelline glands (secreting substances that go to make up the egg yolk and shell) Vt d. - The Vitelline duct (connecting the vitelline gland, which are compact and are situated posterior to the ovary in Taenia. M - The Mehlis gland (A cluster of unicellular shell glands, absent in some species) |
T - Testes (dorso-lateral in D latum. G A - Genital Atrium (lateral in the cyclophyllideans)
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