302 Prof. H. Karsten on Rhynchoprion penetrans. 



apex, is dix'ected backwards, and the two others forwards. (These 

 teeth occur in Pulex irritans in greater numbei", and along the 

 whole length of the organ.) Internally each of the two delicate 

 lateral walls of the channel is furnished with a thickened ridge, 

 very finely transversely striated ; by these ridges a nearly closed 

 tube is formed at the base of the channel. At the anterior, open 

 end of this tube, which is open longitudinally above, a strong 

 spine is attached on each side, the apex of which projects a 

 little beyond the body of the channel. Near these two larger 

 spines there are also on each side four (in P. irritans three) 

 somewhat weaker acicular points, which appear to be the extre- 

 mities of very delicate lamellae attached in a longitudinal position 

 to the base of the channel. Of these, one is even a little broader 

 than the lateral walls of the channel, so that it is seen project- 

 ing beyond these when the organ is lying on its side ; this 

 lamella (which is probably double) is somewhat chitinized, or at 

 least of a yellowish colour, at its anterior extremity, which forms 

 a strongly projecting tooth, whilst the others are so delicate and 

 transparent that they are visible only with very favourable illu- 

 mination, and nothing can be ascertained with certainty as to 

 their form and mode of attachment. 



In Pulex irritans, Linn., the organ, which is very little smaller, 

 has nearly the same structure ; but this is recognizable with dif- 

 ficulty in both species on account of the great delicacy and trans- 

 parency of the individual parts. This piercing- and sucking- 

 organ is not covered by an upper lip, as in the Diptera ; in this, 

 as in the allied Pulices, the labrum is wanting. 



The labium, on the contrary (PI. IX. figs. 3, 4, 7, 8, & 13), is 

 just as completely developed as in the latter; it is as long as the 

 mandibles, which it embraces from beneath, and more or less 

 completely surrounds. The labium is divided, as in P. irritans, 

 into three regions : the lowest part, which is gibbous beneath, is 

 inserted upon the mentum (k, figs. 3 & 4), and is prolonged 

 into an unjointed channel of nearly the same length, open 

 above and anteriorly somewhat cleft. On each of the two short 

 terminal pieces, which are truncated and greatly emarginate an- 

 teriorly, there is seated, as the third part of the labium, a linear- 

 lanceolate, somewhat concave lamella, of the length of the two 

 preceding regions taken togethei', or even somewhat longer ; but 

 this is neither jointed nor beset with bristles as in P. irritans. 

 As these two palpiform appendages are attached by a narrow 

 base to the truncated extremities of the body of the labium, they 

 are readily broken off (PI. IX. fig. 4/), for which reason they 

 were not observed by Duges and Guerin. 



This organ is of the same form and size both in males and 

 females ; nor does the external form of the rest of the body pre- 



