223 



RECENT LITERATURE. 



N. Leon. ' Rechercbes morpliologiques sur les pieces labiales des 

 Hydrocores.' Jassy, 1901. Pp. 1-13 (1). (15 text figs.). 



One of the controverted questions in the morphology of insects is 

 the origin of the labium in Rhynchota ; a summary of this, the latest 

 work on the subject, will therefore be of interest. Ratzeburg, Bur- 

 meister, Chatin, Wedde, and Leon bold that in the formation of the 

 labium, the labial palpi, which are united along the median line, have 

 also taken part. On the other hand, Westwood, Newport, Latreille, 

 Gerstfeldt, and Geise believe that the palpi do not contribute to the 

 formation of the labium. Recently, Heymons, in an extensive work 

 (1899, ' Beitrage zur Morphol. und Entwickelungsgeschichte der 

 Rhyncboten, 1899, Nova Acta Leop. Carol. Acad. Naturf. Halle, Ixxiv. 

 pp. 349-456, plates xv.-xvii. and 5 text figs.), pronounced against their 

 existence, on the ground that in the Rhynchota the labium is com- 

 posed of four segments, and that the palpi are inserted on the third 

 segment, and not on the second, which is homologous with the mentum 

 in the mandibulate insects. More recently Leon has returned to the 

 charge in the abovenamed brochure. 



The learned Rumanian professor declares that Heymons' objection 

 is disposed of when one considers that the labial palpi are not inserted 

 directly on the mentum, but on an intermediate piece {palpufer), in such 

 mandibulates as Phasnia, lapetus, Gryllus, and Silpha, and that in all 

 these the palpi are inserted, not on the second but on third, as in those 

 waterbugs which have a quadrisegmentate labium. The palpi are 

 inserted directly on the mentum only in those mandibulates in which 

 the palpiger is wanting. This leads to the supposition that the quad- 

 risegmentate labium in waterbugs originated from a mandibulate 

 labium provided with a palpiger, and that the trisegmentate labium in 

 other waterbugs is developed from a mandibulate labium lacking the 

 palpigers. 



The submentum is formed by the coalescence of the two cardines, 

 and the mentum by that of the two stipites ; the third segment between 

 the mentum and the ligula is formed by the coalescence of the two 

 palpigers, consequently the labial palpi, even in Gerris and Halobates — 

 where the labium has four segments — occupies its correct morpho- 

 logical situation. The most important comparative-anatomical fact, 

 proving that the appendages described by Leon in Benacus, Zaitha 

 [recte Belostoma] , Gerris and Vdia, are labial palpi, is that the position 

 they occupy on the labium is exactly the place the labial palpi occupy 

 in the mandibulata. 



Leon distinguishes two labial types in waterbugs ; one composed 

 of four segments, the other of three. 



The rostrum is trisegmentate in Spharodema { = Appasus and Diplo- 

 nychus, Rakatra, Laccotrephes, Nepa, Monnnyx, Gelastocoris ( = Gal- 

 guius), Pelocoris, &c., and is of a very similar type throughout the 

 series. The labium appears to be composed, throughout its length, 

 of two symmetric halves, united along the median line. The 



