200 W. H. FURLONGE ON THE PULEX IRRITANS. 



zones, of which all but the two last are nearly equal in width, each 

 composed of two, very thin, curved, semi-transparent plates of 

 chitin, exquisitely striated, polished, and lustrous. The superior 

 plates embrace the back of the abdomen, and descend, on each 

 side, considerably below the medial line of the body. The inferior 

 plates embrace the abdomen proper, and ascend to an equal dis- 

 tance above the medial line, the rounded extremities of the 

 plates thus overlapping each other considerably — the superior 

 plates being the exterior. The seventh pair of plates have a dif- 

 ferent form from the others, and are somewhat triangular in shape, 

 the apices projecting backwards, and receiving between them the 

 terminal segment of the abdomen. This segment is likewise com- 

 posed of two plates, which differ in structure in the male and 

 female animals, as will, afterwards, be more particularly described, 

 when we come to the consideration of the organs of reproduction. 

 It will be sufficient to say, here, that the upper terminal plate, in 

 both sexes, is curved and somewhat triangular in shape, the apex, 

 of course, projecting backwards, and is nearly divided into two 

 equal parts by a large, rounded or oval opening or excavation, 

 which bifurcates backwards to the extremities. In this opening is 

 set the pygidium, as will presently more particularly be described. 

 The lower terminal plate, which, in this segment of the abdomen, is 

 the exterior, is also somewhat triangular in general form, the 

 lateral terminations projecting a little beyond the extremity of the 

 abdomen. 



Owing to the transparency of the structures, it is very difficult to 

 make out, exactly, how the abdominal plates are attached to the 

 underlying epidermis, but it would appear as if the anterior portion 

 only of each plate is thus attached — the posterior portion overlap- 

 ping and playing freely upon the plate lying immediately behind it. 

 But, however attached to the skin, each plate of the series is 

 capable of independent movement in a radial direction, (consider- 

 ing the medial line as containing the central points of attachment 

 of the plates), while each pair — superior and inferior together — 

 frequently move in concert, in a horizontal direction, backwards 

 or forwards, the segments of the abdomen thus, as it were, 

 telescoping into each other. 



The Spiracles. — Considering them as appurtenances of the ab- 

 domen, it will be convenient, here, to describe the external respira- 

 tory organs, or spiracles. Each of the superior abdominal plates 



