THE PYO[DIUM OF THE COMMON FLEA. 231 



and shown in the diagram. At the outer surface of these vertical 

 rods, that is, between them and the internal wall of the follicle, is 

 a delicate membrane which constitutes the outer boundary of the 

 complicated apparatus, and is continuous with the membrane 

 which forms both the upper and the lower surfaces, and fills the 

 spaces between the wedge-shaped projections. This produces a 

 circular chamber strengthened outwardly by the vertical rods, and 

 above and below by the cuneiform projections. If there were 

 nothing more to the intra-foUicular apparatus this chamber would 

 be a simple, circular passage open at the centre, through which 

 the long bristle passes. But the circular region is not open toward 

 the centre ; it is there closed by a slightly inclined membrane, 

 which extends from the tips of the upper wedges obliquely outward 

 to the tips of the shorter lower projections. This membrane closes 

 the circular chamber, and produces a more or less conical space 

 at the centre of the follicle, through which the long filament issues. 

 But whether or not it completes the structure of this part is doubt- 

 ful. I think it does not. But to become positively assured as to 

 that, a study of sections is necessary, and here the expert micro- 

 tomist will find a subject worthy of his steel. And here, too, he 

 will meet with an object that will tax his skill in the illumination 

 of the microscope, and his ability to manipulate the best high- 

 power objectives. For this is not a low-power object. 



But while I am unable to prove to others that my opinion is 

 correct, still that opinion is that this circular chamber is divided, 

 by vertical membranes, into as many cells or compartments as 

 there are wedge-shaped projections in each row, a membrane ex- 

 tending from a cuneiform body above to the one directly below. 

 I am making no positive statement about this minute structure, 

 and it is minute enough to be a delightful task for the lover of the 

 delectable instrument ; I am expressing only an unproved opinion, 

 leaving to the microtomist the pleasure of deciding the question, 

 and, I am free to confess, envying him the skill needed in the 

 delightful work. However, if these vertical membranes exist, and 

 judging from certain optical appearances I think they do exist, 

 then is the pygidium of the despised parasite one of the most 

 remarkable studies with which the microscopist can become 

 acquainted. 



