158 INVERTEBRATE ANIMALS. 
locomotive limbs, as is so commonly the case in the Crustacea. 
The extremity of the abdomen is, however, often furnished with 
appendages which are primarily connected with reproduction, 
but which are often converted into weapons of offence and 
defence. Of this nature are the “ovipositors” of ichneumons, 
the stings of bees and wasps, and the forceps of the common 
earwig. 
dE / 
Fig. 77.—Diagram of the external anatomy of an insect: @ Head carrying the eyes 
and antennz ; 4 First segment of the thorax, with the first pair of legs; c Second 
segment of the thorax, with the second pair of legs and the first pair of wings ; 
@ Third segment of the thorax, with the third pair of legs and. the second pair of 
wings ; e Abdomen, without limbs, but carrying terminal appendages concerned 
in reproduction. 
The organs of the mouth in insects require a brief considera- 
tion, as being in the closest possible relation with their habits 
and mode of life. Two chief types of mouth are recognisable 
in insects, termed respectively the “ masticatory” and “suctor- 
ial,” according as the mouth is fitted for biting and chewing, 
or simply for imbibing fluids. The masticatory mouth is seen 
in perfection in the beetles, in which the following organs are 
