Dr. Karl Krapelin on the Pulicidse. 51 



considerable notch appears at the apex*, although the side 

 lobes thus produced are not jointed off from tlie unpaired piece 

 in the same way as is usually the case, with the labella of the 

 Diptera for example. But if this conception of the structure 

 of the labium of the Rhynchota be correct, a comparison of it 

 with that of the Pulicidse presents no difficulties. A fusion 

 of the longitudinal fissure of the labium of Sarcopsylla (fig. 8), 

 for example^ nearly to the apex, would essentially realize for 

 us the conditions existing in Rhynchota (compare the labium 

 of Cicada in fig. 5). And with this apparent equivalence of 

 the parts an approximately similar physiological application 

 of them would be associated. 



It has already been pointed out that the labium of the 

 Pulicidie has undertaken the guidance of the sucking-tube 

 only in its distal and not in its proximal part. But exactly 

 the same thing may be asserted of the labium of the E,hyn- 

 chota, which in the basal section of the rostrum shows an 

 effacement of the dorsal furrow and decidedly turns down- 

 wards, and thus devolves the guidance of the sucking-canal 

 and of the piercing setge entirely upon the labrum. In the 

 latter circumstance, indeed, there is an essential difference 

 between the proboscis of the Fleas and that of the Rhyn- 

 chota, as in the former the labrum, which has become one 

 of the constituents of the sucking-tube, cannot possibly be 

 employed to envelop the whole apparatus. But precisely 

 this different application of the labrum renders intelligible 

 a further fundamental difference between the two types of 

 proboscis, which must be found in the physiological appli- 

 cation of the maxilla3. In the sucking-tube of the Rhyn- 

 chota, which^ under the double guidance of the labium and 

 labrum, is sufficiently enveloped and protected throughout its 

 whole length, the maxillte might, without damage, be brought 

 in to complete the true piercing-apparatus ; they have become 

 long thin structures, destitute of palpi. Hanking the sucking- 

 tube. In the Pulicidse, on the contrary, in which the basal 

 section of the sucking-tube, in consequence of the peculiar 

 employment of the labrum, was destitute of an envelope, 

 the maxillai^ developed into broad plates (figs. 4 and 7 and 

 \b^m)^ had this important function of protection transferred 

 to them. That under such a change of function the palpi 



* The section across the tip of the rostrum of Notonecta (fig. 14) shows 

 the labium as consisting of two perfectly separate parts. Geise's state- 

 ment that in Corn a the third and fourth joints of the labium are com- 

 pletely cleft, depends, according to my investigations, upon an erroneous 

 interpretation of the conditions coming into view at the tip of the 

 rostrum. 



4* 



