228 ZOOLOGY FOR MEDICAL STUDENTS chap. 



maxillae, but here the two appendages have undergone fusion across the 

 mesiali plane to form the labium. The two cardines are completely fused 

 to form the submentum (s.me). The two stipites have fused except just 

 at their tips to form the mentum (me) and each of them carries its inner 

 and outer lobe — here called respectively glossa (g) and paraglossa (pg). 

 On each side of the labium is a small labial palp (l.p). In addition to 

 the foregoing portions, which can be readily correlated with corresponding 

 portions of the first maxillae, there is present a conspicuous soft tongue- 

 like lingua (sometimes called hypophar5rnx) which springs from the base 

 of the labium on its anterior side, just behind the slit-like mouth opening. 



Finally there is present the labrum (Z) — a plate-like flap of exoskeleton 

 hanging down in front of the mouth and differing in nature from the 

 mouth parts hitherto described in that it has nothing to do with the 

 true appendages. 



An examination of the mouth parts of one of the bees, such as a 

 common bumble-bee (Bombus — Fig. 104, B) shows that here again is the 

 same set of mouth parts. The chief differences are in the maxillae. In 

 the second maxillae or labium the glossae are fused together to form a 

 long tongue — ^the ligula (g) — used for licking up the pollen and traversed 

 along its hinder surface by a deep groove, nearly converted into a tube 

 by its edges meeting, up which nectar is sucked. The paraglossae (p.g) 

 are reduced but the labial palps (l.p) have their two basal joints much 

 elongated and hollowed out along their median surface into a deep 

 groove. When the two palps are approximated together the soft and 

 delicate ligula lies safely protected in these grooves. In the first maxilla 

 the lacinia (Ic) — shaped like the blade of a scythe — is the most conspicuous 

 part, while a small maxillary palp (m.p) is also recognizable. 



In the Mosquitos the females^which alone suck blood — possess the 

 array of mouth appendages shown in Fig. 104, C. The labium (wx.2) 

 is elongated and is given a trough-like form by a wide and deep groove 

 which traverses its anterior surface and serves to contain and protect 

 six dehcate piercing stylets. Of these four represent the two mandibles 

 (m) and the two first maxillae (wx.i).i The remaining two are the 

 unpaired labrum (Z) and hypopharynx (h). Of these the former is pro- 

 vided with a deep, nearly closed-in, groove along its hinder surface so 

 that it forms practically a tube up which the blood is sucked. 



When not in use these piercing organs lie within the groove of the 

 labium. When the mosquito bites the end of the labium is pressed 

 against the skin and it becomes bent upon itself, while the stiff stylets, 



1 A maxillary palp is present (m.p) which in the females of some genera, 

 such as that figured, is much shorter than in others. 



