GENERAL EXTERNAL STEUCTUEE OF INSECTS. 



19 



"ventral," and "lateral." The chitinous parts of the dorsum con- 

 stitute the tergum; of the venter, the sternum; and of the latus, the 

 fleurum. 



The tergum of the -^A-ing-bearing segments usually consists of 

 two plates — a front one or true notum (fig. 4, N) carrying 

 the wings, and a posterior one, which the writer has termed the 

 fostnotum or pseudonotum (PJV), having no connection with the 

 wings. The first is often more or less distinctly marked into three 

 transverse parts called the prescutum (Psc), scutum (Set), and scu- 

 tellum (Scl). In such cases the exposed part of the postnotum is 

 called the postscutellum [Pscl). From either the anterior or the pos- 

 terior margin of the tergum, or from 

 both, a thin transverse plate projects 

 downward into the interior of the 

 thorax for the attachment of muscles. 

 These plates are the phragmas {Aph 

 and Pph). The notum supports the 

 wing on each side by two small lobes, 

 the anterior and posterior notal tcing 

 processes {ANP and PNP). Behind 

 the latter is the attachment of the 

 axillary cord (AxC) or basal ligament 

 of the wing. A large V-shaped ridge 

 on the under surface of the notum hav- 

 ing its apex forward is the " entodor- 

 sum." (A better name would be 

 enfotergum.) 



The pleurum consists principally of 

 two plates, the epistemum (fig. 4, Eps) 

 and the epimerum {Epm)' lying before 

 and behind a vertical groove, the pleural suture (PS) , which extends 

 from the pleural coxal process (CxP) below to the pleural wing 

 process (WP) above. The pleural suture marks the position of a 

 heavy internal ridge, the pleural ridge or entopleurum. The epi- 

 merum is connected with the postnotum (PJV) behind the base of the 

 wing. These parts occur in almost all insects. In some of the lower 

 ones another plate is present in front of the episternum which may 

 be called the preepisternum {Peps)."- Lying along the upper edge of 



" Objection may be made to the use of the term " preepisternum " on the 

 ground that it combines a Latin prefix with a word compounded of Greek ele- 

 ments. The same may be urged against " prephragma," " postphragma," "pre- 

 paraptera," and " postparaptera," words introduced by the present writer in a 

 former paper on the thorax (Proc. TJ. S. Nat. Mus., XXXVI, 1909, pp. 511-595). 

 However, we are barred from making up equivalent terms with the Greek pre- 

 fixes pro and meta because these are used to designate the first and the third 



TnC- 



Fig. 4. — Diagram of generalized 



thoracic segment, left side. 



