ANNULOSA I INSECTA. 267 



ORDER III. PAUROPODA. In this order is only an extra- 

 ordinary little Myriapod, described by Sir John Lubbock 

 under the name of Pauropus. The body is only one-twentieth 

 of an inch in length, and consists of ten somites, furnished with 

 scattered setae. There are only nine pairs of legs, of which 

 one pair is carried by the 3d segment, whilst the 4th, 5th, 6th, 

 and yth segments carry each two pairs of legs, and may there- 

 fore be regarded as really double. The head is composed of 

 two segments, and is not provided with jaw-feet. The witennae 

 are five-jointed, bifid, with three long multi-articulate appen- 

 dages. The body is white and colourless, and there are no 

 tracheae, so that respiration must be effected entirely by the 

 skin. Pauropus is found amongst decaying leaves in damp 

 situations, and species have been described both from Britain 

 and America. It is separated from the Chilopoda by its small 

 number of legs, the absence of foot-jaws, and the composition 

 of the antennae out of no more than five joints. 



DISTRIBUTION OF MYRIAPODA IN TIME. About twenty 

 species of Myriapoda are known as fossils, the oldest example 

 of the order having been found in the Carboniferous epoch. 

 From rocks of this age several species of Chilognathous Myria- 

 pods have been discovered. They belong to the genera 

 Xylobius and Archiulus, and have been placed in a special 

 family under the name of Archiulidce. The occurrence of 

 air-breathing articulate animals (both Arachnida and Myria- 

 poda] in the Carboniferous period is noticeable, as being con- 

 temporaneous with the earliest known terrestrial Molluscs. 



CHAPTER XXXIX. 

 INSECTA. 



GENERAL CHARACTERS OF THE INSECTA. 



CLASS IV. INSECTA. The Insecta are defined as articulate 

 animals in which the head, thorax, and abdomen are distinct ; 

 there are three pairs of legs borne on the thorax ; the abdomen 

 is destitute of legs ; a single pair of antenna is present ; mostly, 

 there are two pairs of ivings on the thorax. Respiration is 

 effected by trachece. 



In the Insecta the body is divided into a variable number of 

 definite segments, or somites, some of which are furnished 



