Xll] MOUTH-PARTS OF INSECTS 245 



second maxillae of the Cockroach, but as a rule traces of all the 

 gnathites may be found though often much altered. The mouth-parts 

 of Insects have been grouped as follows : (i) BITING. This kind 

 of mouth is found in the Aptera, the Orthoptera, the Neuro- 

 ptera and the Coleoptera (v. below), in which orders there is as 

 a rule no very great difficulty in recognising the various parts which 

 have been described in the Cockroach. As an example of the great 

 variety presented by the mandible, those of the male Stag-beetle, 

 Lucanus cervus, may be mentioned. In this animal the mandibles 

 may equal in length the whole of the rest of the body, (ii) SUCKING. 

 This kind of mouth is found in the Lepidoptera or Butterflies. 

 Here the mandibles are rudimentary, but the laciniae of the first 

 maxillae are much elongated ; each lacinia is grooved and so applied 

 to the other as to form a tube, and in some cases the two halves of 

 the tube are locked together by minute hooks; this tube is generally 

 coiled into what is sometimes termed the proboscis. The palp 

 of this maxilla is absent or rudimentary. The labium composed 

 of the second maxillae is an important structure in the larva or 

 caterpillar, as it forms the spinnerets through which the silk of 

 the cocoons is excreted, but in the adult it is represented only 

 by its palps which persist as large hairy structures. The hollow 

 tube formed by the maxillae is well adapted to suck up the fluids 

 on which the Lepidoptera live. The suction is performed by a 

 powerful muscular sac called the suctorial stomach, which is a 

 lateral outgrowth of the oesophagus and communicates with it. 

 (iii) PIERCING AND SUCKING. The Diptera or Flies possess both 

 sucking and piercing organs, which are as a rule somewhat unequally 

 developed. The basal portion of the labium or second maxillae is 

 much elongated and takes the form of a fleshy protuberance which 

 to some extent ensheaths the other parts. In the House-fly, Musca 

 domestica, the piercing organs have been lost, but in the Gnat or 

 Mosquito they reach a high degree of development. These parts are 

 overlaid by a somewhat enlarged labrum and between this and within 

 the grooved labium the pointed stylets lie. The hypopharynx*is 

 well developed and is easily distinguished since it takes the form 

 of a sharp style. Two pairs of lateral stylets, identified by some 

 as the modified mandibles and first maxillae, also exist and the 

 maxillary palp acts as a sensory organ. The Hemiptera or Bugs 

 have a very similar set of gnathites in correspondence with their 

 habit of boring into animals or plants to feed on their juices. In this 



* See page 257. 



