Snake flies (Raphidioptera), alder flies (Megaloptera: Sialidae) and also some myxophagan coleopterans share the same, peculiar telotrophic organization of their ovarioles usually referred to as ovarioles of the Sialis-type. Ovariole ontogenesis in Raphidia sp. is described and the basic events that lead to the formation of germ cell clusters and their subsequent transformations are reported. It was found that the major cellular events during ovariole formation in Raphidia and Sialis are essentially the same. Discrepancies concern details of germ cell cluster formation, differentiation of cystocytes within clusters and their location within the developing tropharium. Based on these results the hypothetical model of the Sialis-type ovariole formation, previously presented by KING and BNING (1985) is verified. A hypothesis on the mechanisms of oocyte determination in telotrophic ovaries is also presented.
Different theories conceptualise dyslexia as either a phonological, attentional, auditory, magnocellular, or automatisation deficit. Such heterogeneity suggests the existence of yet unrecognised subtypes of dyslexics suffering from distinguishable deficits. The purpose of the study was to identify cognitive subtypes of dyslexia. Out of 642 children screened for reading ability 49 dyslexics and 48 controls were tested for phonological awareness, auditory discrimination, motion detection, visual attention, and rhythm imitation. A combined cluster and discriminant analysis approach revealed three clusters of dyslexics with different cognitive deficits. Compared to reading-unimpaired children cluster no. 1 had worse phonological awareness; cluster no. 2 had higher attentional costs; cluster no. 3 performed worse in the phonological, auditory, and magnocellular tasks. These results indicate that dyslexia may result from distinct cognitive impairments. As a consequence, prevention and remediation programmes should be specifically targeted for the individual child's deficit pattern.
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