No. 1774. THORAX OP ItYAIENOPTERA—MODGRASS. 41 



segment, those of the thorax corresponding with the "mikrothorax," 

 "stenothorax," and "cryptothorax," of Verhoeff. 



It is only in the neck region that a sufficient structure is found to 

 warrant the idea of an extra segment. Many entomologists as well as 

 myriopodists have believed, as first suggested by Huxley, that the 

 sclerites in the walls of the neck, often highly developed in the lower 

 orders, are the rudiments of a fourth thoracic segment. This sup- 

 posed segment was named by Verhoeff the "mihroihorax.' ' But yet, 

 no actual proof has been adduced of the segmental nature of this group 

 of sclerites. Some students of the subject think that the plates in 

 question are derived from the labial segment of the head, others from 

 the front of the prothorax, while still others claim that they arise 

 from both of these sources. No one has discovered a separate neck 

 segment. If the neck sclerites belong to the labial segment, then this 

 segment must carry the name " microthorax " if the term be used at 

 all. To the writer it now seems preferable to dispense with this 

 appellation altogether, and to substitute the term cervicum, as used by 

 Crampton (1909), to designate the neck and its plates; distinguishing 

 the latter as the cervical sclerites. This involves no theory concerning 

 the nature of these parts. The writer thus retracts whatever doubtful 

 notions on the "microthorax" he may have expressed in former 

 papers (1909, 1910). 



The terms used in this paper to designate the principal parts of the 

 body and of each thoracic segment are classified in the following 

 tables. The phragmas, as will be shown later (pp. 57 to 64), are 

 really intersegmental structures, or at least are developed interseg- 

 mentally, and hence, should be classed as such, though in adults they 

 become associated with either the segment before or behind them. 

 Since the first segment of the thorax is often so very different from the 

 other two, on account of the reduction of its parts, a wing-bearing 

 segment is given as a complete example of a thoracic segment. 



PRINCIPAL PARTS OF AN ADULT INSECT. 



Head. — Composed of seven consolidated segments. 



Cervicum. — The neck region, including the cervical sclerites, derived 



perhaps from both the head and the prothorax. 

 Thorax. — Composed of three segments. 

 Prothorax. 

 Anterior j)hragma. 

 Mesothorax, including the mesothoracic apotomal plates when 



present. 

 Middle jphragma. 

 Metathorax, including the metathoracic apotomal plates when 



present. 

 Posterior yhragma. 

 Abdomen. — Composed of ten or more segments, except in Hymen- 

 optera, where the first is transferred to the thorax. 



