TRACHEATA 335 
coxal processes are wanting. Similar processes occur internal 
to the base of each of the twenty-two pairs of legs in Scolo- 
pendrella. 
Some very remarkable spherical protuberances of the 
integument near the middle line are found in JMMachilis and 
Campodea, projecting between the abdominal appendages. 
They are twenty-two in number in the former genus, a pair pro- 
jecting behind the sterna of the first, sixth, and seventh segments, 
and two pairs behind those of the second, third, fourth, and 
fifth. These protuberances appear to be extended by the 
forcing into them of some of the blood. They have special 
muscles which retract them, and as a rule they are found in 
the retracted condition. They probably serve as respiratory 
organs. They are absent in Lepisma and Japyx. 
The number of ganglia in the abdomen is eight, except in 
Campodea, where only seven have been described. In the 
last-named genus the nervous system is in intimate connection 
with the hypodermis. Machilis has a pair of large compound 
eyes. The Thysanura are all provided with salivary glands 
and Malpighian tubules, and the heart has nine pairs of ostia. 
The tracheal system is fairly well developed; in Machilis a 
pair of stigmata are found on the meso- and meta-thorax, and 
on each of the abdominal segments from the second to the 
ninth ; the tracheae do not anastomose. 
The primitive position of the Aptera is shown (i.) by the 
absolute absence of wings, (ii.) by the direct developement,—this 
is, however, shared by several other orders of insects,—(iii.) by 
the presence of abdominal appendages, (iv.) by the very slight 
developement of the cuticle, and (v.) by the general resemblance 
of some of the genera to the larvae of higher forms. This is 
recognised by the application of the term campodiform to the 
larvae of most insects with direct developement, and to some 
of those, e.g. certain families of beetles, with indirect. 
OrpER 2, ORTHOPTERA, 
CHARACTERISTICS.—Lnsects with direct developement. Prothorax 
Sree. Lbiting mouth parts. Wings usually unequal, the 
anterior pair small and hard, the posterior membranous. 
