1878.] 291 [Burgess. 



The Anatomy of the Head, and the Structure of the 

 Maxilla in the Psocid.e. By Edward Burgess. 



Westwood, in his " Classification," x describes the maxilla of the 

 Psocidae — the family of minute insects which includes the well- 

 known " book-louse '*' — as " elongated, fleshy at the tip, armed with 

 a long, slender, curved, horny process, arising from the base, and 

 longer than the maxillse." This description, although correct, like 

 most of its author's, as far as it goes, fails to call attention to the 

 really unique structure of the maxilla in this group of insects. Other 

 writers 2 have given us no fuller or more satisfactory description, a 

 fact for which the minute size of the Psocidse and the consequent 

 difficulty of examination perhaps accounts. I have recently carefully 

 studied the general anatomy of the head in Psocus and Atropos, 3 of 

 which I offer the following description. 



The maxilla in Psocus is hinged to the head by a small obscure 

 piece, which is immovably soldered to a larger joint. The first piece 

 represents, probably, the cardo of a typical maxilla (Plate 8, figs. 1, 

 3, 4 and 6, c), and the second, the stipes (p.). The stipes bears 

 outwardly the four-jointed maxillary palpus, while inwardly is hinged 

 a thick, fleshy lobe, broad at the base, but soon contracting and 

 curving inwards (figs. 4 and 7). The tip is flat and has a broad, 

 oval outline on the inside, and is strengthened by several imbedded 

 chitinous rods and other pieces Cfig. 7). This lobe, by its position and 

 shape, is doubtless homologous with the ordinary outer maxillary lobe, 

 or galea, of the other Orthoptera. Behind the lobe, that is, between 

 it and the tongue, lies the " horny process " of Westwood's descrip- 

 tion, or " fork," as I shall call it. This is a slender, more or less 

 curved, chitinous rod, with a forked, bifid tip, and two or three times 

 «as long as the outer lobe (fig. 7, etc.,/.) The distal portion of the 

 fork, about one-third or less of its length, projects through the lining 

 membrane of the mouth. At this point the fork is stoutest, and from 

 it it tapers to either end, the outer portion being stouter than the in- 



i Vol. II, p. 17, fig. 59,4- 



2 It will not be out of place to refer to the only paper we have on the anatomy of 

 any species belonging to the Psocida?, viz. : " Ueber die Eingeweide der Biicherlaus 

 (Psocus pulsatorius) " von C. L. Nitzsch, Germar's Mag. d. Entoinologie, iv, 276. 

 Tab. ii. The* author excellently describes and figures the reproductive and diges- 

 tive systems of the Book-louse, but does not refer to the mouth organs or salivary 

 glands. Mr. Scudder, Psyche, IX, 49, has erroneously described the maxilla of 

 Atropos as two-jointed. 



3 See Psyche, Vol. n, No. 43. 



