28 



are a number of sclerites which are considered by some 

 writers to be merely appendages of the abdomen ; other 

 writers hold that certain of these sclerites represent sterna^ 

 and certain others, terga. 



It is not within the scope of this work to enter into any 

 discussion of the matter. We shall describe the parts as if 

 there were eleven segments ; but wish the student to under- 

 stand that the so-called eleventh segment may be merely an 

 appendage of the tenth ; and that what is described here as 

 the ninth and tenth segments have not been considered as 

 such by certain very high authorities. 



First abdominal segment. — The dorsal and ventral 

 parts of the first abdominal segment are widely separated by 

 the caudal part of the cavities for the insertion of the third 

 pair of legs. 



The ventral part of this segment is dove-tailed into the 

 metasternum, and at first sight would be taken for a part of 

 the thorax. 



On each side in the dorso-lateral part of this segment, 

 there is a large opening which is closed by a very delicate 

 membrane; these are the auditory organs ; the membrane is 

 the tympanum. 



Just cephalad of each auditory organ there is a small 

 opening ; these are the first pair of abdominal spiracles. 



Second to eighth abdominal segments.— Each of 

 the abdominal segments, from the second to the eighth in- 

 clusive, is ring-like in form, and without appendages. 



In each of these segments the lateral margins of the ter- 

 gum join the pleura * without any suture. Near the cepha- 



* The lateral part of a segment is termed the pleurum ; in the same way that 

 the ventral part is called the sternum ; and the dorsal part, the tergum. By 

 some writers the entire dorsal part ol an insect is called the tergum , the lateral 

 part, the pleurum ; and the ventral part, the sternum. These writers apply the 

 terms tergite, pleurite, and sternite respectively, to tne dorsal, lateral, and ster- 

 nal regions of each segment. 



