1916] Thoracic and Cervical Sclerites of Insects 77 



of Doleriis and are seen to be much reduced in size (Fig. 12, es, 

 emi). From the above facts, it seems very probable that the 

 large sclerite in sawfiies, which Snodgrass, '10, calls the "pro- 

 episternum," is really a large lateral cervical sclerite, fused with 

 the episternum and in some cases with the epimeron also. The 

 fact that an internal process is present at the point of articula- 

 tion of the "proepisternum" with the head (Fig. 15, ap), sig- 

 nifies that this plate is a cervical sclerite, since a similar process 

 is found on the lateral cervicals of several other insects as in 

 Gryllus, Forficiila, etc. 



When the epimeron is absent in the prothorax of sawfiies, 

 Snodgrass, '10, considers the internal process or pleural arm, as 

 apparently not the homologue of the pleural arm of the other 

 segments, since it does not arise between the plates (Fig. 14, 

 pla). This may be true, but in all cases the pleural arm is joined 

 to the furca of the furcasternite as in other segments and in 

 other insects. If the epimeron has apparently disappeared in 

 the prothorax of some sawfiies, it may be represented by a part 

 of the pleural arm itself, especially if it be true that the pleural 

 arm is formed by an infolding of the integument. Thus it 

 would seem more probable that the pleural arm in the pro- 

 thorax of sawfiies, in which the epimeron is absent, is the 

 homologue of the pleural arm of other segments and of other 

 insects. 



Several theories have been formulated to account for the 

 origin of the cervical sclerites. 



Straus-Durckheim, '28, suggested that the cervical sclerites 

 represent the remains of two segments, situated originally 

 between the head and prothorax. He designated them by the 

 term "pieces jugulaire." 



Newport, '39, considered them as detached portions of the 

 prothorax and called them the prothoracic "paraptera. " 



Lowne, '70, regarded the cervicals as a part of the labial 

 segment or last cephalic segment of the head. This theory 

 was later adopted and supported by Huxley, '85, Comstock, 

 '02, Riley, '04 and others. Although Riley, '04, regards the 

 lateral cervical sclerites as the pleurites of the labial segment of 

 the head, he also states that part of the pleural region of the 

 labial segment is already included in the head capsule. Lowne, 

 '70, applied the terms "condyle" to the lateral cervicals and 



