350 APHANIPTERA. 



named goniocephalus by Taschenberg, on account of an angular 

 projection on the forehead, which, however, is not always very 

 apparent. It is probably the Ceratophyllns leporis of Curtis. 



The mouth-organs of the flea consist of a pair of mandibles 

 with toothed edges, a tongue, an underlip with two palpi, which, 

 when joined, form a hollow tube in which the tongue lies ) their 

 structure is well shown in P. avium. In this the tongue has been 

 removed, and the mandibles are two long delicate bristles, which 

 lie close together at the top. They are so transparent that they 

 are difficult to photograph, and in the female of P. avium they are 

 scarcely visible ; they are the two faint lines on the left centre. In 

 P. g07iiocephalus^ on the other hand, the mandibles are large, strong 

 blades, doubly serrated along the edges. There are also two 

 maxillae, generally triangular plates, each with a four-jointed palpus. 

 Regarding the labial palpi, Westwood* says, "these are three-jointed. 

 Latreille described them as three-jointed ; Curtis described them 

 as four-jointed; while Dujes figured them as five-jointed. Theobald 

 says they are four-jointed ; while Taschenberg, whose descriptions 

 of fleas are by far the most accurate of any I have yet seen, says 

 they are four-jointed, and adds, " Bouche has quite wrongly des- 

 cribed them as five-jointed, and Kolenati has fallen into a similar 

 error." It is impossible to tell, by the examination of an entire 

 flea mounted in balsam, what is the real number of joints in these 

 labial palpi, though in the maxillary palpi the joints are distinct 

 enough. I did not try to decide the question until a few months 

 ago, and then I found it almost impossible to get any living fleas, 

 except goniocephalus from the rabbit, and aviu7n from poultry ; but 

 from these two species I found that in the latter they are five- 

 jointed, as described by Bouche, Dujes, and Kolenati ; while in 

 the former they are only two-jointed, a number of joints which, so 

 far as I am aware, has not been mentioned by anyone. In fact, I 

 suspect it to be the old story of the Chameleon, " You all are 

 right, you all are wrong," and that the naturalists who thus differ 

 have dissected and described different species of flea. 



The eye, when present, lies generally about the centre of the 

 head, and is a simple ocellus ; sometimes; however, it is very near 

 the lower margin. Close behind it lies the antennae, in a kind of 



* Class. Ins, 



