TRACHEATA 335 



coxal processes are wanting. Similar processes occur internal 

 to the base of eaoh of the twenty-two pairs of legs in ScolO' 

 •pemdrella. 



Some very remarkable spherical protuberances of the 

 integument near the middle line are found in Maahilis 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. 



Okder2. ORTHOPTERA, 



Chaeacteeistics. — Insects with direct developement. Prothorax 

 free. Biting mouth parts. Wings usually unequal, the 

 anterior pair small and hard, the posterior membranovs. 



