228 THE PYGIDIUM OF THE COMMON FLEA. 



intends to suggest, but something quite different. Other observers 

 had noted these spines, and indeed had figured them as stout, 

 tapering bodies arising from a circumvallate depression, to the 

 base of which each was said to be attached by a socket-joint. 

 The fact is that no such socket-joint, nor any structure resem- 

 bling it, is present on the inter-areolar surface of the pygidium . 

 " As an example of erroneous interpretations," says Dallinger 

 in his edition of " Carpenter, " " the representation of the 

 pygidium of a flea by some leading sources of information of 

 a few years ago may be instanced. It was a special test of 

 many authors, and has been carefully figured ; this shows that 

 it was not an accidental error, which it might have been if it 

 were merely an ordinary object ; it is an error depending in 

 all probability on a faulty system of illumination. Moreover, 

 the error cannot be attributed to the object-glasses of the time, as 

 it is a low-power object, and the low powers of that day were quite 

 as good as those lately in use. In the descriptions and in the 

 drawings, often beautifully executed, the hairs proceeding from 

 the centre of the wheel-like discs are represented as being ' stiff 

 and longish bristles,' thick at one end and tapering off to a point. 

 And the small hairs round (sic) are described as 'minute spines' ; 

 in the drawing they are like the spinous hairs of an insect, and 

 have the usual socket-joint at the base. In reality, the 'stiff and 

 longish bristle ' is an extremely long and delicate filament, totally 

 unlike a bristle, being not tapered but of nearly uniform thickness. 

 The ' minute spines ' are in reality very curious hairs, and, as 

 far as we at present know, unlike any others. They are delicate, 

 lambent, bulbous hairs." 



These "stiff and longish bristles," which issue from the areolae, 

 appear to be fragile, and are, as a consequence, readily broken, 

 when they are observable on the preparation as stout, truncated 

 filaments, usually with no trace of decreasing diameter. But when 

 they are unbroken they certainly do taper; and do so conspic- 

 uously, at least with the specimens which I have seen. If a true 

 bristle must taper, then are these true bristles. 



The flame-shaped hairs are narrowed with a regular gradation 

 from the somewhat bulbous base to the usually curved and acumi- 

 nate tip. But if the classical socket-joint of these inter-areolar 



