858 



SIPHON APTERA AND COLEOPTERA 



ring to the antennal groove is the gena. A process of this area may be pro- 

 longed backwards, so as to meet the hind edge of the post-antennal part of 

 the head, and so to close the antennal groove below in those species which 

 possess a closed antennal groove. 



The occipital area carries usually three rows of bristles, the first near the 

 base of the antennae, the second in the middle, and the third near the hinder 

 edge of the head, which are continued forwards on to the frons, and probably 

 delineate the four segments of which the head is composed. 



Anterior and ventral to the frons and gena lies the perioral ring, which 

 carries the mouth appendages, which consist of a labrum (epipharynx), 



mandibles, maxillae, and palps, hypo- 

 pharynx, and labium with palps. 

 There does not appear to be a 

 separate clyp^us. 



The labrum (variously known as 

 epipharynx, hypopharypx, and by 

 other names) is a hollow prolonga- 

 tion of the dorsal wall of head and 

 pharynx. In front it is closed, while 

 behind it opens into the coelom. 

 Ventrally it shows a groove, con- 

 verted into a canal when it is articu- 

 lated with the mandibles laterally. 

 The mandibles consist of basal seg- 

 ments attached to the sides of the 

 mouth, and an anterior portion which 

 projects freely forwards, and shows 

 fine serrations anteriorly. The inner 

 aspect of the mandibles possesses a 

 groove, converted into a trilobed 

 channel by articulation with the 

 fellow of the opposite side and the 

 hypopharynx. 



The maxillae are triangular chiti- 

 nous plates, each possessing a four- 

 jointed maxillary palp. The labium 

 (which, of course, represents the 

 second maxillae with their palps) is 

 single posteriorly, where it is attached 

 to the perioral ring, while in front it 

 is divided into two one-to-thirteen 

 jointed palps (labial palps), which 

 form a sheath or rostrum for the 

 other mouth-parts. 



The hypopharynx consists of a 

 basal portion, which is a chitinous 

 plate concave ventrally, extending 

 forwards in the head from the infra- 

 oesophageal ganglion to the mandi- 

 bulo-basal articulation, and an anterior portion, which projects from the 

 baSal portion forwards, and contains the canal from the salivary pump. 



This anterior portion of the hypopharynx articulates laterally with the 

 mandibles, and its canal, opening ventrally, forms the triradiate canal men- 

 tioned above, which is continuous with the salivary groove on the mandibles. 



The thorax is composed of the usual three divisions, but there are no signs 

 of scutellum or post-scutellum. There is generally one, but there may be 

 two or three rows of bristles on each segment. The pronotum may have a 

 comb. The metanotum may be dentate or serrate apically. Laterally the 

 metathorax is typical, showing a sternite, episternite, and epimerite, while the 

 mesothorax shows a sclerite, divided into two by an internal incrassation 

 running from the coxa upwards. These two divisions represent the episternite 



Fig. 450. — Xenopsylla cheopis : Male. 



(After Jordan and Rothschild, Journal 

 of Parasitology.) 



I, Labrum, mandibles, and labial 

 palps (at the junction of the last named 

 with the head is seen the triangular 

 maxilla) ; 2, maxillary palpi ; 3, antenna; 

 4, pronotum; 5, mesonotum; 6, meta- 

 notum; 7-12, ordinary abdominal ter- 

 gites; 13, seventh tergite with bristle 

 (behind this is seen the small eighth 

 tergite); 14, ninth tergite, with sensory 

 plate; 15, tenth tergite ; 16-24, sternites 

 of abdominal segments; 25-27, meta- 

 sternite; 28, mesosternite ; 29, pro- 

 sternite. 



