210 



ORTHOPTERA 



CHAP. 



they have been made use of for purposes of classification, though 

 no functional importance was attached to them. Meinert, 

 however, discovered^ that there are foetid glands in this 

 situation, and Vosseler has recently shown ^ that the folds are 

 connected with scent -glands, from which proceed, in all pro- 

 bability, the peculiar odour that is sometimes given off by the 

 earwig. The forms destitute of the folds, e.g. Labidura, are 

 considered to have no scent glands. There is a very peculiar 

 series of smooth marks in the earwigs on the dorsal aspect of 

 the abdominal segments, and these are present in the glandless 

 forms as well as in the others. 



The internal anatomy has been to some extent investigated 

 by Dufour and Meinert. Dufour dis- 

 sected F. auricularia and Labidura riparia, 

 and found ^ that salivary glands exist in 

 the latter Insect (called by him Forficula 

 gigantea), though he was unable to discover 

 them in the common earwig. According 

 to Meinert,^ there are, however, salivary 

 glands affixed to the stipes of the maxillae 

 in F. auricularia, while (in addition ?) L. 

 riparia possesses very elongate glands seated 

 in the middle or posterior part of the breast. 

 The alimentary canal is destitute of con- 

 volutions, but oesophagus, crop, and gizzard 

 all exist, and the intestine behind the 

 stomach consists of three divisions. The 

 Malpighian tubes are numerous, 30 or 40, 

 ^V^'Zi^^Zy^"" and elongate. The respiratory system is 

 not highly developed. Earwigs the Euro- 

 pean species at least have, as already mentioned, very small 

 powers of flight ; the tracheal system is correspondingly small, 

 and is destitute of the vesicular dilatations that are so remarkable 

 in the migratory Locusts. 



The three thoracic spiracles ^ are readily observed in living 



^ NaturhistorisTc Tidsskrift, 3rd ser. ii. 1863, p. 475. 



2 Arch, mikr. Aiiat. xxxvi. 1890, p. 565. 



3 Ann. Sci. Nat. xiii. 1828, p. 337. 



^ Naturhistorisk Tidsskrift, 3rd ser. ii. 1863, p. 475. 



^ Some writers are of opinion that there are only two thoracic spiracles in Insects, 

 considering the third as belonging really to the abdomen. Looking on the point as 



