The morphology of the British Prostriata, with particular reference toIxodes hexagonusLeach. III

Abstract

1. The spiracular plate is made up of three layers, (a) the outermost non-porose plate, which varies in thickness, being thicker where the (b) intermediate layer of pedicels fuses towards the outside, and thinner over the goblets. The innermost layer (c) is of even thickness, and corrugated.2. The ostium is bounded by the columella dorsally and by the lower lip ven-trally, both of which are continuous with the thickened antero-ventrally placed macula.3. The ostium opens into a subostial space which in turn passes into the atrium. The ventral and ventro-lateral walls are thrown into two folds about midway along, and then anteriorly and posteriorly merge to form a single lobe. The musculature associated with the atrium is described.4. On morphological grounds it appears that the ostium is incapable of opening and closing, and it is suggested that only opening muscles—the dorsal and ventral atrial muscles—are present.5. The distribution of the main tracheal trunks is described.6. Hailer's organ in the female ofI. hexagonusconsists of a trough and a capsule; the former bears six hairs divisible into types I–IV and the latter contains seven tapering sensillae. This pattern is applicable to both the male and the nymph: in the larva one type III sensilla is missing from the trough and only 4 sensory hairs are present in the capsule.7. A description of Haller's organ in the BritishIxodesspecies is given, and it is shown to be of systematic value.8. The status of species possessing ‘trough-nosed’ capsules is discussed, and the validity of giving such species generic rank does not appear to be justified. As far as the material investigated is concerned there seems little difference in the sexes, with the exception ofI. murisandI. loricatus, nor has any correlation been established between the structure of the organ and host specificity.