684 EXTERNAL ANATOMY OF INSECTS. 
readier elevation and depression of this joint. In the 
Orthoptera the tetramerous genera are those which 
Linné called Tettigonia amongst his Grylli (Acrida, 
Conocephala, Pterophylla, &c.); Gryllus monstrosus also, 
and in the Neuroptera, Raphidia belong to this section. 
Trimerous insects are those whose éarsi consist of only 
three joints. Amongst beetles the Lady-birds (Cocc?- 
nella) are remarkable for this structure, but in them the 
claw-joint is also diarticulate, so that strictly speaking 
they are ¢etramerous ; in the Orthopterous Order the mi- 
gratory locusts (Locusta) belong to this section, as like- 
wise Gryllus and Gryllotaipa : in the first of these genera 
is an appearance of there being more joints in the ¢arsus, 
‘because there is more than one cushion below the first *. 
To this section also belong the great majority of the He- 
miptera, excluding only those tribes that connect the 
two sections of the Order constituting the two Linnean 
genera Nepa and Notonecta; the Libellulina likewise 
belong here, as do also the Scorpionide and Scolopen- 
drida. 
Dimerous insects are those that have ¢wo joints in 
all their ¢avsz. Such are the Pselaphide in the Co- 
leoptera Order >; in the Hemiptera—Belostoma and No- 
tonecta ; inthe hexapod Aptera—Pediculus ; in the octo- 
pod—the Acari of Linné; in the myriapod—Zulus ; and 
in the Arachnida—-the Araneida. F: 
Monomerous insects are those which have only a single 
tarsal joint. Only ene Coleopterous and also one He- 
mipterous genus is so distinguished : the first is Clambus 
> Vor. II. p. 325—. 
> Dr. Leach says there are ¢hvee joints in this tribe. Zuol. Afise. 
iit. 80. 
