MARINE ARTHROPODS 295 



communication between one insect and another. In them are 

 also located the organs of hearing, and, possibly, those of other 

 senses. 



The mouth varies very considerably in different insects, but is 

 often supplied with a pair of mandibles or biting jaws, and, below 

 them, a pair of maxillae or chewing jaws, both pairs being jointed 

 to the head in such a manner as to be capable only of horizontal 

 movements. Above and below these jaws are, respectively, the 

 upper lip or labrum, and the lower lip or labium, the latter having 

 appended to it a pair of jointed feelers called the labial palpi, 

 and an additional pair of palpi are also frequently attached to the 

 maxillse, and therefore called the maxillary palpi. 



These organs of the mouth of an insect are modified in various 

 ways according to the functions they are called upon to perform. 

 Thus, in bees, the upper lip, as well as the mandibles, are adapted for 

 chewing, while the maxillae and the labium are grooved in such a 

 manner that when brought together they form a tube through which 

 fluids may be sucked into the mouth. Also, in the butterfly and 

 the moth, the maxillae are not constructed for chewing, but consist 

 of two channelled rods which, when approximated, form a long 

 tube or proboscis employed for suction ; and in these insects the 

 labial palps are large for the protection of 

 the proboscis, which is retracted and closely 

 coiled between them when not in use. Fur- 

 ther, in the bugs, the labium is long and 

 tubular, while the mandibles and maxillse 

 are often modified into sharp, stiff bristles 

 that work within the tube, the whole thus 

 forming a combined piercing and sucking 

 arrangement. 



The leg of an insect is built up much in 

 the same manner as that of the typical crus- 

 tacean. It consists of a basal hip joint or 

 coxa, a ring segment or trochanter, a thigh 

 (femur), a shin (tibia), and the tarsus or 

 foot of several joints which terminates in a j? IG 220. TUB LEO 

 claw or claws, and is often provided with o? AN INSECT 



sucking-pads. The wings, when present, are 



attached to the second and third segments of the thorax, if two 

 pairs, but if, as in the case of the house fly, the insect has only one 

 pair of wings, these are always appended to the second segment. 



