268 



Arthropoda. 



never sunk into it ; sometimes, indeed, it is situated on a stalk-like 

 process of the protliorax. The usual mouth-parts are present, and of 

 these, the mandibles are powerful biting organs. In some Hymenop- 

 tera — but these are in the minority — the " tongue," which is formed by 

 the concrescence of the ligulse, is elongate and gutter-like ventrally, and 

 surrounded by a tube formed of the long, flattened, labial palps and 

 blades of the first maxillae (only a single blade of each being present) ; 

 by means of the tongue and its sheath, sweet liquids are sucked up 

 into the mouth. The prothorax is but feebly developed, the dorsal is 

 separated from the ventral portion, and is firmly fused on to the meso- 

 thorax, whilst the latter (with the first pair of legs) is movable. Meso- 

 thorax and metathorax are usually immovably united, but in the Saw- 

 flies and Wood-wasps they are freely articulated. The legs are character- 

 ised by the size of the coxae ; the trochanter is often divided into two 

 joints (in the Tenthredinidee, Uroceridas, Cynipidae and Ichneumonidae) ; 

 the first joint of the pentamerous tarsus is much longer than the 

 following (metatarsus). The front pair of wings is almost always 

 much larger than the hind pair ; both are veined, but not very 

 closely; those of the same side are connected by a row of small 

 hooks on the anterior edge of the hind wing, which fasten into 

 the curved hinder edge of the front onej thus, during flight, the 



Fig. 221. A Abdomen with ovipositor of one of the TJrooeridEe. The spine (o) is 

 pushed out from the groove (d) in which it lies when at rest ; this groove is continued from 6 

 into the two long lobes c, which surround the termuial portion of the spine. B Transverse 

 section of the spine and the lobes, enlarged, a b and a' V lobes (= c in ^), c d, e and e' the 

 three acicular pieces of the sting. — ^After Graber. 



two act as one continuous lamina. At the base of the front wing, 

 there is a projecting scale which covers the base of the hind 

 wing. In all the Hymenoptera, the first abdominal segment is 

 im m ovably united with the metathorax, and in the majority (i.e., in 

 all with the exception of the Tenthredinid^ and Uroceridee), there is 

 a deep constriction between this and the following abdominal 

 segments; the abdomen is thus said to be stalked, but it must 

 not be forgotten that the constriction occurs not between the two 

 regions, but in the abdomen itself; the segments following the 

 constriction are usually narrower than the first. At the hinder 



