A half a century ago, R. T. Leiper described a new species belonging to the genus Fasciola from specimens which he collected from hippopotami at the Murchison Falls, on the Victoria Nile in Uganda, in the summer of 1907. This species, Fasciola nyanzae, was found in the bile ducts of the liver, and in most instances the specimens were somewhat macerated owing to the length of time that had elapsed before the animal could be recovered from the water. Nevertheless, the characteristic shape of these liver flukes and the restriction of the branched testes to the anterior third of the body made it possible to recognise them as being different from all other species of the genus known at that time.
The development of Paramphistomum sukari Dinnik in a snail host is described with the emphasis laid on the succession of redial generation.The sporocyst gives birth to about twenty to thirty rediae. These rediae of the first generation commence with the production of daughter rediae then enter the second phase of their productivity during which they produce cercariae. The daughter rediae, or the rediae of the second generation, repeat these two phases during their lives, commencing with redial production and after that changing to the production to cercariae. Both the first- and second-generation rediae are able to produce a few daughter rediae at the end of their life. There is evidence that the subsequent generations of rediae are also able to give birth to daughter rediae and cercariae.As a result the successive generations of rediae maintain the infection in an intermediate host for a long time, probably as long as the infected snail can survive.
The whole life cycle of Paramphistomum microbothrium Fischoeder, 1901, found in cattle of Kenya, East Africa, has been established experimentally.In laboratory conditions, the eggs hatched miracidia on the 14th to 16th day, if they were kept in water at a temperature of 26–28° C.In a snail, Bulinus alluaudi (Dautzenberg), kept at the temperature of 18–20° C., the miracidium developed into a sporocyst, the elongated body of which, containing young rediae, reached a length of 3·6 mm. in about 2 weeks.The first rediae which emerged from a sporocyst were observed on the 14th day, and on the 20th day the first generation rediae began to produce second-generation rediae. From the 28th day onward the first-generation parent rediae ceased to produce daughter rediae and began to develop cercariae only. This period of production of cercariae by the redia lasted about 30 days, and when the life of the first-generation rediae drew to its close, the old rediae developed a few daughter rediae again.Cercariae began to emerge from the first-generation rediae 30 days after exposure of the snail to miracidia. The cercariae left the parent redia in a very immature state and further development occurred in the liver of the snail. The emergence of cercariae from the infected snail began on the 43rd day after exposure to miracidia. Shortly after emerging from the snail, the cercariae attached themselves to vegetation and encysted.Development of rediae of the second, third, fourth and apparently more successive generations followed an identical course to that outlined for the rediae of the first generation. As a result the successive generations of rediae maintain the infection going in an intermediate host and the infected snails were continually shedding cercariae as long as they lived. In the laboratory experiments the life span of some of the infected snails exceeded a year.In cattle infected experimentally P. microbothrium reached maturity and began passing out the eggs about a 100 days after the encysted cercariae were fed to the animals.
The development of Carmyerius exoporus Maplestone in the snail Anisus nata-lensis Krauss is described with the emphasis laid on the redial and cercarial productivity of the rediae of the first and subsequent generations.The miracidium gives rise to one sporocyst. From 25 to 32 germinal cells present in the miracidium, only six to eleven develop into embryo balls in the sporocyst and, of these, only three to nine develop into rediae of the first generation.The redia of the first generation gives birth to daughter rediae and cercariae. No alternation in the development of redial and cercarial embryos was noted in the rediae of C. exoporus and a small number of redial embryos was observed to develop alongside the more numerous cercarial embryos throughout the life of the first generation rediae.The rediae of the second and subsequent generations also give birth to daughter rediae and cercariae.The cercariae leave their parent redia when they are still immature and continue the development in the snail tissue.
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