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Ultrastructure of spermatazoa and prostate gland of Avitellina lahorea135were observed enclosed within membrane bound (1992, 1994 a and b) in other species, could bebodies of apical cytoplasm of vaginal epithelium. The distinguished without any clear morphologicalyoung spermatid exhibited a roughly circular nucleus demarcation between them but exhibited distinctivewith partially condensed chromatin. The various ultrastructural characteristics (Fig. 1c). These regionsultrastructural features of spermatozoon are given are described below:below.Region I: This region exhibited an apical cone ofSperm crest: TEM micrographs revealed a crest electron-dense material. The cortical microtubuleslike body in the ultrastructure of spermatozoon of A. formed a continuous layer of dens and sublahorea.According to Ba and Marchand (1994a), the membranous material. The axoneme appearedpresence of crest like body or bodies represents the surrounded by a fine discontinuous sheath of anfront part of sperm, whereas the end without it electron-dense material and an electron-lucentrepresents the posterior extremity. The sperm crest in cytoplasm.cestodes showed variability in different species. In R.Region II: This region exhibited a central axoneme, aserrata, H. nana and A. delafondi, the crest-like bodiesthin layer of electron-lucent cytoplasm and a single orare of same thickness but are different in length. On thetwo bundles of spiral cortical microtubules, whichother hand, in M. expansa, M. benedeni and T. ovilla,sometimes cover each other partially and form athe crest-like bodies are not only same in thickness butdiscontinuous layer of electron-dense and subalsoin length. Ba and Marchand (1994b) havemembranous material.described two crest-like bodies of unequal thicknessand length in R. tunetensis. However, in A. Region III: In this region, central axoneme was foundcentripunctata, these authors have described a simple to be surrounded by a fine layer of lucent cytoplasm andand single crest-like body.a continuous sheath of electron-dense material. Thecytoplasm appeared electron-lucent and sub-dividedCortical microtubules: The cortical microtubules raninto several compartments by irregularly-spacedall along the length of spermatozoon and formed apartitions of electron-dense material.continuous layer of dense sub-membranous material.They were observed to be spiralized and the angle-of- Region IV: This region is marked by the presence ofspiralization appeared more or less marked. The nucleus. The nucleus appeared to be fine, compact andmitochondria and acrosome were conspicuously coiled in a spiral around axoneme. It enveloped theabsent. The microtubular elements constitute a axoneme once or twice, interposed itself between thecharacteristic feature of most vertebrates and cortical microtubules and closely contacted the plasmainvertebrate spermatozoa. The absence of acrosome has membrane.been construed as an unusual characteristic oftrematode sperms. Burton (1967) has attributed that theRegion V: This region appeared to be wide with aincompatible length of sperm and the size of ovum, andpointed end. Disorganization and disappearance ofthereby, the limited space for the penetration of spermaxoneme and intracytoplasmic partitions of electron-into the latter, provide little advantage for the presencedense material could be seen in this region.of acrosome. Moreover, a spermatozoon in trematodes The partitions of proteinaceous materials were presentdoes not penetrate an ovum; instead the plasma in cytoplasm. The mitochondria were conspicuouslymembranes of gametes fuse and sperm internal absent. The absence of mitochondria suggested that thestructures pass into ovum. Considering the unusual sperm may be deriving energy through glycolysis. Theultrastructural features such as the absence of production of lactic acid in tissues of A. lahorea andacrosome, mitochondria and the stiff spindle-like Stylesia globipunctata (Venkatesh and Ramalingam,length of spermatozoon, a similar phenomenon viz., 2006) serves as evidence for the above speculationapposition of gametic membranes during fertilization, (Ramalingam et al., 2004). Ba and Marchand (1994 a,may be also conjectured to occur in this species of b) also described intracytoplasmic partitions ofcestode parasites.proteinaceous materials.Cytoplasmic partitions: The cytoplasm of A. lahorea Cortical tubules and fertilization: The spermatozoawas observed to be of low electron-dense nature. From of A. lahorea exhibited only the apical cone-likethe anterior to the posterior end of spermatozoon, five structure, and acrosome is completely absent. Thecontiguous regions, as suggested by Ba and Marchand presence of cortical microtubules in the anterior region