TV. H. FURLONGE ON THE PULEX IRRITANS. 195 



less to enlarge the orifice, probably first formed by the mandibles and 

 maxillary palpi, and thus to promote the flow of blood. A high powei 

 and very careful illumination, is required to resolve the structure ot 

 this organ, to which I would desire to direct the attention of some of 

 the accomplished observers numbered amongst the members of this 

 club, the more especially as the result of my own observations leads 

 me to differ materially from the conclusions of Mr. Gosse. In a 

 popular description of the trophi of the flea,* this distinguished 

 naturalist states that the labrum or upper lip, as he terms the 

 organ, consists of a narrow chitinous blade, having both its edges 

 studded with teeth similar to those of the mandibles, but set in a 

 single row. It seems to me, however, that the organ is not a chiti- 

 nous blade, but a fleshy, and, I think, muscular, proboscis, perforated 

 throughout by a canal, and that certainly, it is not surrounded by 

 a row of teeth. 



We now proceed to the description of — 



The Thorax, which, as in insecta generally, is formed in three 

 segments, the pro-thorax, the mezo-thorax, and the meta-thorax, 

 each division carrying one pair of legs. 



The pro-thorax, or anterior segment, consists of three thick plates 

 of chitin. The superior plate embraces and defends the back, rest- 

 ing upon it like a saddle, of which the truncated flaps descend on 

 each side, to the angle of the head piece, at which point they meet ; 

 and are united to, the two lateral plates, nearly pyramidal in shape 

 and convex outwardly, which enclose, and in fact constitute, those 

 parts of the pro-thorax to the anterior angles of which the first 

 pair of legs is articulated. The three plates composing the pro- 

 thorax (as is also the case with the plates of the other segments,) 

 are attached to, and in reality form parts of, a thick membranous 

 skin, enveloping the whole animal, and which, it may be remarked, 

 seems to serve a purpose analogous to that of the coat of thick buff 

 leather worn by the knights and men-at-arms of old beneath their 

 armour. But only the anterior half of the upper or back plate, is 

 thus attached to the membranous skin, the unattached posterior 

 half overlapping the second segment of the thorax, and moving 

 freely upon it. From the line of junction of the upper plate with 

 the skin, a series of about a dozen stiff bristles or seta?, emerge at 

 regular intervals and project backwards. These setas pass through 

 the chitinous substance of the plate in a horizontal direction, through 



* Evenings at the Microscope— p. 178. 



