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THE PYGIDIUM OF THE COMMON FLEA. 



through which the long bristle projects, tlie dome itself bearing 

 some minute external appendages. The areolse are by no means 

 the simple, uncomplicated objects they are commonly described 

 and figured to be. They have been looked upon by microscopists 

 as low-power objects, as Dr. Dallinger describes them, but they 

 will 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. 17. 

 Diagram 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. The 

 cuneiform projections (they are not elevations as commonly des- 

 cribed) converge towards the centre from a comparatively wide 

 band of encircling chitin, and each is outwardly continued toward 

 the bottom of the follicle by a curved, rod-like body, which at the 

 base becomes continuous with a second set of wedge-shaped pro- 

 jections, often less strongly chitinous than the upper row, and 

 always rather shorter. There is not a single row of these cunei- 

 form projections which have so long been used as a test for 

 definition, and which Dr. Van Heurck says Dujardin figures as 

 being round. There are two rows entirely distinct from each 

 other, but connected exteriorly by the vertical rods referred to. 



