THE PYGIDIUM OF THE COMMON FLEA. 229 



hairs can be proved to be an error of observation, as can be 

 easily done, then it is not unlikely that there are other structural 

 points about the organ which may have been overlooked or mis- 

 interpreted. In fact, there seem to be several. 



Of some of those to be mentioned here there is absolutely no 

 doubt ; of a single one there must be doubtful acceptance until 

 the microtome can be brought to bear on the pygidium, when the 

 problem may be readily solved. I have not even the skill of a 

 novice in the use of the microtome, and those of my friends and 

 correspondents who have attempted to section the pygidium have 

 failed, either on account of the horny character of the subject, or 

 because of the lack of sufficient material. When sectioned it 

 will not be what Dr. Dallinger calls a low-power object ; even in 

 its totality it is far from being that. 



The areolae, or those superficially wheel-like bodies which, 

 in number from thirty-two to thirty-eight (Van Heurck), constitute 

 the double, somewhat reniform organ called the pygidium, are not 

 the simple bodies which they are usually supposed to be. The 

 ordinary statement of the books is, as Dr. Van Heurck puts it in 

 the fourth edition of his work on The Microscope, that, "The pygi- 

 dium of the flea is composed of two lobes and exhibits from 

 thirty-two to thirty-eight long, stiff hairs implanted in the centre of 

 each of the areolae, each one being surrounded by a row of little 

 cuneiform elevations. The inter-areolar spaces are covered with 

 small spines. A good objective should show these areolse clearly 

 defined in all their parts, and the elevations should appear cunei- 

 form, and not round as they are figured by Dujardin." This is 

 not all of the structure as I see it with the best objectives of 

 Reichert, Zeiss, and of Spencer. 



Each areola is in reality a follicular depression, varying in 

 dimensions to a degree perceptible even without the use of the 

 micrometer, but averaging, perhaps, about 1/3000 inch in depth ; 

 and each contains, not only the long central, bristle-like filament 

 and the cuneiform projections, which are said to form a single 

 row, but a somewhat complex,' strongly chitinous system of rods 

 and wedges and membranes, the whole apparatus being covered 

 by an elevated, membranous dome about as high above the gene- 

 ral surface as the follicle-is deep below it, and with a central eye 



