Progenetic plerocercoids

Fig. 8.15. Monthly variation in the ovarian content of the three-spined stickleback, Gasterosteus aculeatus, parasitised with the progenetic plerocercoids of Schistocephalus solidus. (After Meakins, 1974.)...

With the exception of a few species with progenetic plerocercoids (e.g. Schistocephalus) it is only within the definitive host that cestode tissue develops in a strobilar direction, and it is self-evident that strobilar differentiation must be induced by factors present in the intestinal environment. Clearly, any number of known parameters of the intestine (Fig. 3.1, p. 37)... 

Fig. 10.1. Progenetic plerocercoid of the pseudophyllidean Schistocephalus solidus, (a) Enlarged view of plerocercoid showing genital anlagen. (ft) Whole plerocercoid removed from fish.

This was the first cestode species cultured to maturity in vitro (786) and it has proved to be a valuable experimental organism. The progenetic plerocercoid (Fig. 10.1) already contains well-developed anlagen of the... 

The Pseudophyllidea contain many well-known species which infect birds and mammals and whose plerocercoids occur in cold-blooded vertebrates, especially fish. Several have progenetic (p. 214) plerocercoids, e.g. Schistocephalus and Ligula, and furthermore these larvae contain sufficient food reserves (such as glycogen) to satisfy the energy and synthetic needs of maturation without additional external nutrients being provided. Such larvae provided useful experimental models for early work in this field, as maturation could be achieved in vitro once sterility and the appropriate environmental conditions were provided (786, 787, 788). Although these... 

The plerocercoids of L. intestinalis (Figs. 8.14 (p. 220) and 10.3) are also progenetic and larvae are relatively large, usually about 100-200 cm in roach (787). This large size makes them especially suitable for experimental work and a number of valuable biochemical and metabolic studies have been carried out (26, 502, 515). 

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