The Journal of microscopy and natural science . the use of themicrometer, but averaging, perhaps, about 1/3000 inch in depth ;and each contains, not only the long central, bristle-like filamentand the cuneiform projections, which are said to form a singlerow, but a somewhat complex, strongly chitinous system of rodsand wedges and membranes, the whole apparatus being coveredby an elevated, membranous dome about as high above the gene-ral surface as the follicle-is deep below it, and with a central eye 230 THE PYGIDIUM OF THE COMMON FLEA. through which the long bristle projects, tlie dome itself
The Journal of microscopy and natural science . the use of themicrometer, but averaging, perhaps, about 1/3000 inch in depth ;and each contains, not only the long central, bristle-like filamentand the cuneiform projections, which are said to form a singlerow, but a somewhat complex, strongly chitinous system of rodsand wedges and membranes, the whole apparatus being coveredby an elevated, membranous dome about as high above the gene-ral surface as the follicle-is deep below it, and with a central eye 230 THE PYGIDIUM OF THE COMMON FLEA. through which the long bristle projects, tlie dome itself bearingsome minute external appendages. The areolse are by no meansthe simple, uncomplicated objects they are commonly describedand figured to be. They have been looked upon by microscopistsas low-power objects, as Dr. Dallinger describes them, but theywill prove themselves worthy of study with the highest-power ob-jectives at our disposal. The structure of these wonderful bodies,as I see it, is shown in the accompanying diagram, Fig. 17 :—. Fig. of an areola from the Pygidium of a Flea. The walls of each follicle are vertically fluted at regular inter-vals, and the upper margin is, as a result, broadly crenated. Thecuneiform projections (they are not elevations as commonly des-cribed) converge towards the centre from a comparatively wideband of encircling chitin, and each is outwardly continued towardthe bottom of the follicle by a curved, rod-like body, which at thebase becomes continuous with a second set of wedge-shaped pro-jections, often less strongly chitinous than the upper row, andalways rather shorter. There is not a single row of these cunei-form projections which have so long been used as a test fordefinition, and which Dr. Van Heurck says Dujardin figures asbeing round. There are two rows entirely distinct from eachother, but connected exteriorly by the vertical rods referred to. THE PYO[DIUM OF THE COMMON FLEA. 231 and shown in the diagram. At the ou
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