NO. 1687. THE TJIOltAX OF IXfiECTti—^yOUaRAHfi. ^^\ 



C). The pkniruni consists fundamentally of a i)late s(ien<>thened 

 internally by a heavy, inllecteti, median, vertical iid<j,"e to support the 

 wing ab()^■e and to i-arry the le<i,' below. Tiius it has become divided 

 into the episternum anteriorly and the epinierum posteriorly, sepa- 

 rated externally by the pleural suture along- the line of the internal 

 pleural ridge. (See text figs. 3 and 4.) The wing support forms a 

 Aving process and the coxal support the coxal process of the pleurum. 

 In front of the episternum there' is in some of the lower insects a pre- 

 episternuin. Along the base of the wing parapteral j^lates are de- 

 veloped. In front of the coxa is the trochantin, a plate possibly 

 derived from the sternum, articulating above with the episternum 

 and below forming the ventral articulation of the coxa. 



7. The wing is hinged to the notum on the two notal wing proc- 

 esses, and is supported from below upon the wing process of the 

 pleurum. 



In the Ephemerida and Odonata the chitinous wing base is di- 

 rectly continuous with the Avails of the thorax. In all other orders 

 there is an articulation formed by several axillary sclerites in the 

 membranous base of the wing. Three of these are of definite char- 

 acteristic shajie and of constant recurrence in all the orders and are 

 present in the elytra of beetles and the halteres of flies. In the 

 Orthoptera and Hymenoptera a fourth sclerite occurs, and this num- 

 ber may -be regarded as the full complement. AYhen four are present 

 the first and fourth articulate with the anterior and posterior notal 

 wing processes, respectiveh% the second articulates with the wing 

 process of the pleurum. while the third suppcu'ts the anal veins and 

 is concerned in the })lication of the anal region when~ the latter is 

 folded. AVhere the fourth is absent the third articulates with the 

 posterior notal ])rocess. 



VII. SI»Er'IAI. niAKACTEKS OF THE ORDERS. 



A. ('ini.oroDA. 



A study of the Chilopoda in connection with a study of the insect 

 thorax brings out the following two interesting features: 



1. A serial examination of the pleurum of M ecistocejjhalus (20), 

 Scoloj)oeryptops (21), Litliohius (22), and Cermatia (23) appears 

 to indicate that only one plate {PI) of the numerous pleurites on 

 each segment in the lower Chilopoda (20) persists in the higher 

 (23), and this plate is suggestive of being the one from which the 

 episternum and epimerum of the Hexapoda are formed. Compare 

 Cermatia (23, PI) Avith the Melanoplufi nymph (56, Eps and Epni). 



2. The trochantin {Tn) appears to be originally a lateral subdivi- 

 sion of the sternum (20). The part behind the coxa disappears 

 (21, 22) AAdiile the part in front extends upAvard t<^ the j)leurites. In 

 Cermatia (23), lioweA^er, it is gone entirely. 



