74 Annals Entomological Society of America [Vol. IX, 



without first working out the musculature of these sclerites. 

 Whether the spiracle belongs to the segment in front, or behind 

 it, is still a disputed question, although it seems very probable 

 that each spiracle belongs to the segment behind it. 



In the dorsal neck region of Periplaneta there is a small 

 sclerite (Fig. 5, dcs), which seems to be homologous with a 

 similar sclerite found in the dorsal intersegmental region 

 between the pro- and mesothorax of Corydalis (Fig. G, i). 

 This would indicate that the neck sclerites and the inter- 

 segmentalia are homologous. 



Voss, '04, Heymons, '95, and Palmen, '77, have proposed 

 various theories concerning the spiracles. From a study of 

 the musculature, Voss, '04, claims that they belong to the seg- 

 ment in front of them. From a study of their embryology, 

 Heymons, '95, concluded that they He in the anterior portion 

 of their respective segments, but may secondarily move forward 

 and become attached to the segment in front of them. Palmen, 

 '77, thought that the first thoracic spiracle might be either 

 pro- or mesothoracic, varying in different insects. It is gen- 

 erally agreed among most workers that the third thoracic 

 spiracle belongs to the first abdominal segment. Of the three 

 theories mentioned, Heymons' seems to have the most support, 

 but more investigation on this point is necessary before it 

 can be definitely settled. 



Cervical Sclerites. Embedded in the soft neck region of 

 most insects are found a varying number of sclerites, differing in 

 size and shape in different insects (Fig. 3, Ics, vcs). These 

 sclerites are designated by the term "Cervical Sclerites" 

 (Huxley, '85) or " microthoracic sclerites" (Verhoefif, '02-'04), 

 etc. In this paper the term cervical sclerites will be adopted 

 for these neck plates. 



There can be no question that the cervical sclerites of 

 one insect are in general homologous with the cervicals of other 

 insects. But difficulty arises as to the origin of these neck 

 plates and their homologies. They may be either detached 

 portions of the head or of the prothorax or of both, while some 

 have even considered them as the remains of one or more 

 primitive segments. Each of these four theories has its own 

 adherents and which one is correct, it is impossible to say at 

 present. The cervical sclerites furnish support for the head 



