W. H. FURLONGE ON THE PULEX IRRITANS. 23 



which are thickened and fringed with curved bristles projecting 

 backwards. In their normal position these plates incline inwards 

 towards each other, the convex sides being outwards, so that their 

 fringed margins unite and form a ridge or crest, rising very little 

 above the edges of the cavity, and completely closing the opening 

 in which they are placed. These sheath plates gradually taper 

 downwards like leaves, and terminate in stout short stalks, which 

 are attached to curved chitinous bands similar to those after- 

 wards to be described as moving the sheath of the penis. When 

 these organs are in action they are pushed backwards and upwards, 

 and assume an erect or nearly parallel position, as shown in the 

 figure. This movement is accomplished by means of appropriate 

 muscles attached to the chitinous processes just described. 



The Prehensile Organs (Fig. 7) consist of a pair of strong claws, 

 or nippers, situated within the concave sheath plates, to the stalks 

 of which they appear to be attached, so that when the sheath 

 plates are extruded the forceps come up with them. These organs 

 strikingly resemble the terminal joints of the large claws of the 

 lobster, excepting that one of the extremities of each is broad and 

 square, while the other is bluntly pointed. They are composed of 

 chitin of a deep reddish-brown colour, and appear to be solid or 

 homogeneous in structure, and although attached to the stalks of 

 their sheath plates, they are capable of independent movement in a 

 manner precisely similar to that of the analogous terminal joint of 

 the lobster's claw. I may observe that one of the plates, with its 

 accompanying forceps, is sometimes extruded or retracted sooner 

 than the other, though they generally move in unison. 



The Sheath of the Penis. — When the plates and forceps have 

 been protruded the sheath of the penis begins to emerge between 

 them, and finally assumes a position nearly erect, or slightly curv- 

 ing backwards, which, it may be remembered, was shown in the 

 large drawing of the male pulex accompanying my previous paper. 

 The sheath possesses a very remarkable structure. It consists of a 

 fleshy organ, relatively of very considerable size, which is surrounded 

 for about two-thirds of its circumference by a very thin, polished, 

 curved plate of chitin, which serves to sustain the fleshy organ 

 within, the posterior portion of which projects beyond the edges of 

 the investing plate. 



At the extremity of the organ, which is triangular in section, 

 the terminal edges of the chitinous plate are capable of being drawn 



