Dr. Murai Éva szerk.: Parasitologia Hungarica 25. (Budapest, 1992)

to the results obtained by Pandey (1972) for the parasite of goat/dog origin. Unfortunately, the location of cysts was not mentioned in either of the above two studies. It is quite surprising that in the region where these studies were carried out, there is no rigid ecological/geographical segregation through any barrier or quarantine restriction. The frequent interstate movement of animals and the use of common grazing land are common practices of animal farmers. Therefore, such differences may be due to the greater variability and biotic potential of £. granulosus combined with the effect of host species. The results of the present study on the prépaient period do not agree with previous reports from India (Gill and Rao 1967, Pandey 1972) as well as from other geographical regions (Thompson et al. 1984). Generally the gravid segment has been reported to appear between 40-48 days p.i. (Gemmel 1962, Smyth et al. 1967), but recent studies on the in vivo and in vitro development of different strains of E. granulosus demonstrate considerable variability in the onset of egg production (Kumaratilake et al. 1983, Thompson et al. 1984). In similar type of study, Thompson (1977) established the occurrence of British horse and sheep strains by investigating the differences existing in the developmental pattern of protoscoleces in dogs. The horse strain was found to lag behind the sheep strain and took two days longer to produce eggs. Similarly, the present study has shown that the liver isolate has a slower rate of development and takes two days longer to produce eggs than the lung isolate. The foregoing discussion indicates that liver and lung materials of buffalo origin differ from each other as well as from other strains reported from different geographical regions. On the basis of differences observed in the developmental pattern and also in biochemical composition (Irshadullah et al. in preparation), it is suggested that these variations are either habitat induced or due to two distinct biological variants, as genetically different protoscoleces have also been reported from different cysts of the same host (Lymbery and Thompson 1989). The term "strain" is now commonly accepted when referring to intraspecific variants of uncertain taxonomic status. It is possible that such differences develop in E. granulosus due to self-fertilization and clonal proliferation in a particular habitat. In a recent study, on the basis of cross-transmission experiments Cook (1989) suggested that there in only one form ofE. granulosus in the U.K. This idea has, however, been contradicted by some workers (McManus et al. 1989, Lymbery and Thompson 1989) and it was suggested that the results of cross-transmissions do not overshadow the possibility, reported previously on various grounds, that different strains may exist. Thus, on the basis of just one parameter it is difficult to accept or reject the existence of different strains and, therefore, further studies are certainly required on strain characterization using the criteria suggested by Thompson and Lymbery (1988). On the basis of above discussion it is emphasized that the variability existing in the onset of egg production bears enormous significance in formulating an effective drug treatment programme.