NO. 2 ENCYCLOPEDIA OF INSECT ANATOMY — SNODGRASS 7 



back (whence the adjective dorsal), it is useful to restrict the term 

 tergum to a major plate of the dorsum. Many entomologists use 

 "tergite" for a segmental back plate, but the suffix ite in biology means 

 "a part of," as in somite and podite. Properly, therefore, a tergite 

 should be a division of a tergum ; if the word tergite is used for the 

 entire segmental plate we are left without a word for the parts of 

 a subdivided tergum. 



Nottim is the Latinized Greek equivalent of tergum (from Gr. 

 noton). It is properly used for the back plates of the thorax in com- 

 bination with the Greek prefixes pro-, meso-, and meta-. 



Pleuron: The term is derived from the Greek pleuron, pleura, 

 a rib. The pleura in general may be defined as the lateral sclerotiza- 

 tions of the body segments between the tergal and sternal plates. In 

 insects such sclerotizations are present principally on the thoracic 

 segments and are best developed in connection with the wings. 



The insect pleuron seems to have no prototype in the other arthro- 

 pods. In the primitive crustacean Anaspides the back plates of the 

 thoracic segments are continuous over the dorsum and down the 

 sides, and they support the legs on their lower margins. In the 

 Malacostraca the carapace cuts out the back of the dorsal plates, 

 leaving the lateral parts as plates supporting the legs. These plates 

 might be called "pleurites," but they are simply remnants of the 

 primitive terga. The diplopods likewise have no pleural plates sepa- 

 rate from the terga. In the chilopods, plates in the pleural region 

 above the coxae appear to be derivatives of the coxae. 



Among the insects, the pleural sclerotization of the thoracic seg- 

 ments is never continuous with that of the dorsum. In the Protura 

 and Thysanura, the terga and sterna are separated by wide mem- 

 branous areas. The pleural sclerotization in each segment consists 

 only of a pair of narrow sclerites concentrically arched over the base 

 of the coxa; these are termed the anaplciiritc and the cataplcurite. 

 The same type of pleural sclerotization occurs in some larvae of the 

 lower pterygotes and in adult termites. The presence of two supra- 

 coxal pleural arches in the thoracic segments may be regarded as a 

 primitive condition in the insects having no relation to anything in 

 the other arthropods. 



In the pterygote insects the pleural sclerotization becomes more 

 or less continuous over the sides of the thoracic segments but shows 

 many modifications. Typically it is marked by a conspicuous groove, 

 the pleural sulcus, extending upward from the leg base; this forms 

 a strong ridge on the inner surface, on the lower end of which the 



