INSECTS OE HBXAPODA. 



139 



legs, attached to the thoracic region on its ventral surface. This 

 feature ■will at once separate them from all other Arthropods. 

 Eespiration is tracheal, the openings or spiracles heing slit-like 

 apertures along the sides of the abdomen, in addition to two 

 pairs on the thorax. The typical mouth of an insect is de- 

 scribed in chapter vii. This is a biting mouth, a type of 

 oral structure we find in many injurious insects. Others are 

 provided with a piercing mouth, and live upon plant sap and 

 animal blood, often causing serious loss to the farmer and stock- 

 breeder, as well as spreading such human diseases as malaria, 



/ , , an 



Mouth Parts of Insects. 



A, Biting mouth parts ; b, suclting, and c, piercing mouths : I, upper lip ; m, man- 

 dibles ; Tjia:, maxillie ; m;j, maxillary palpi ; la, lower lip ; Z^, labial palpi ; an, antenijii.*. 

 (Nicholson.) 



yellow fever, filariasis, and basilero. The third form of mouth, 

 the sucking mouth, usually prevents those insects possessing 

 it from doing any damage ; but there are some moths whose 

 proboscis is so hardened that they damage fruit in South Africa. 

 Those groups with this latter type of oral structure aid more 

 or less in the fertilisation of plants. It will be chiefly, then, 

 amongst the biting and piercing mouthed insects that the injuri- 

 ous species will be found. But we must bear in mind that many 

 suctorial mouthed insects have mandibulate larvse, which can 

 do as much damage as the true mandibulate groups. Many 



