THE DIPTERA. 



367 



the mouth is constructed upon the same plan as that of the 

 Semiptera, so far as the conversion of the labium into an 

 organ of suction is concerned ; but usually the metamorpho- 

 sis of the gnathites is carried still further, and the maxillae 

 have palps. Thus, in the Fleas, which are parasitic on mam- 

 mals and birds, what appears to be the labrum is an elon- 

 gated, slender style, which lies between the two elongated 

 mandibles. The first maxillae are broad triangular plates, 

 each with a four-jointed palp. The second maxillae (labium) 

 are represented by a short median lamella, which bounds the 



Fig. 106. 



Fig. 107. 



Fig. 106.— The head, A, and parts of the mouth, B, C, of Sphinx ligustri.—a, anten- 

 na; 6, epicranium ; c, cornea; d, clypeus posterior; e, lahrum;/, mandible; g, 

 maxilla ; h, maxillary palpus : k, lahial palpus. B, base of the maxillae with the 

 mandibles and labrum. C, lateral view of the same. (After Newport.) 



Fig. 107.— Vanessa atalanta. — Inner or concave surface of the apical portion of the 

 right maxilla : a, transverse muscles ; b, canal ; c, papillae ; d, hooks which join 

 the maxillae. 



mouth behind, and is provided with two long palps, which 

 resemble knife-blades, and are imperfectly divided into four 

 joints. The three somites of the thorax are distinct, and the 

 two hinder ones have lamellar appendages, which possibly 

 represent wings. The abdomen has ten somites. 1 



In those dipterous insects which are termed JPtipipara, 

 which are apterous, or nearly so, and parasitic upon mam- 



1 See L. Landois, " Anatomie des Hundeflohes," 1866. 



