VIII 



STRUCTURE 



535 



in a broad sense with maxillae of mandibulate Insects, and the 

 outer pair with mandibles, is probably correct. Mecznikow, who 

 studied the embryology, 1 supports this view for Heteroptera, 

 but he says (t.c. p. 462), that in Homoptera the parts of the 

 embryo corresponding with rudimentary maxillae and mandibles 

 disappear, and that the setae are subsequently produced from 

 peculiar special bodies that are at first of a retort-shaped form ; 

 the neck of the retort becoming afterwards more elongate to form 

 the seta ; also that in the Heteropterous genus Gerris the 

 embryology in general resembles that of Homoptera, but the 



FIG. 256. Mouth - parts of 

 Hemiptera. (After 

 Wedde.) A, Section of 

 the head and proboscis of 

 Pyrrhocoris apterus : dr, 

 gland; i.g, infra - oeso- 

 phageal ganglion ; Ib, 

 labium ; Ir, labrum ; m, 

 muscles ; m 1 , muscle (de- 

 pressor of labium) ; m 2 , 

 muscle of syringe ; ph, 

 pharynx ; s, setae ; s.g, 

 supra - oesophageal gang- 

 lion ; sp. dr, salivary 

 gland ; spr, syringe : B, 

 transverse section of pro- 

 boscis of Pentatoma nifi- 

 pes, at third joint of 

 sheath : m, m, muscles ; 

 md, mandibular seta ; mx, 

 maxillary setae ; n, nerve ; 

 p, the sheath or labium ; 

 tr, trachea. 



development of the setae is like that of other Heteroptera (t.c. p. 

 478). This discontinuity in the development of the Homopterous 

 mouth has since been refuted by Witlaczil, 2 who found that the 

 retort-shaped bodies really arise from the primary segmental 

 appendages after they have sunk into the head. We are there- 

 fore justified in concluding that the mouth-parts are at first 

 similarly developed in all Hemiptera, and that this development 

 is of a very peculiar nature. 



Smith is convinced that there are no traces of mandibular 

 structure in any Hemiptera. 3 On the other hand, numerous 

 entomologists have supposed they could homologise satisfactorily 

 various parts of the Hemipterous trophi with special parts of the 



1 Zeitschr. wiss. Zool. xvi. 1866, p. 389. 2 Arl. List. Wien. iv. 1882, p. 415. 

 3 Tr. Amer. Phil. Soc. xix. 1896, p. 176. 



