25 



two fleshy lips ; this is one of the openings of the respira- 

 tory system , these openings are called spiracles. When, as 

 in this case, a spiracle is surrounded by a circular sclerite, 

 such a sclerite is termed a pcritrcme. 



In the membrane connecting the mesothorax with the pro- 

 thorax there is on each side a spiracle. This spiracle is 

 covered by the free margin of the pronotum. In this case 

 the peritreme is developed on the ventral side of the spiracle 

 into a prominent papilla. 



Make a drawing of the lateral parts of the mesothorax and 

 metathorax. 



Review. The thorax consists of three segments, which 

 are named, beginning with the cephalic, prothorax, mesothorax, 

 and metathorax. 



The body-wall of each of these segments is believed to 

 consist typically of ten sclentes. Of these,/*?*//- pertain to the 

 dorsal part of the segment ; tivo to each lateral part ; and two 

 to the ventral part. 



The dorsal sclerites are named, beginning with the ceph- 

 alic, prcesciitum, scutum, scutellum, &\\& postscutellum. 



Of the lateral sclerites, the cephalo-ventral one is the epi- 

 sternum, the caudo-dorsal one, the epimeron. 



The ventral sclerites are known as the sternum and the 

 sternellitm. The sterna of the three thoracic segments are 

 designated as the prosternum, mesosternum, and metasternum 

 respectively; and the sternella as the prosternellum, mesoster- 

 nellum, and metasternellum. 



In most insects the sternella are so reduced in size as to 

 be indistinguishable. 



Sometimes there is also present near the base of the leg a 

 distinct antecoxal piece 



The dorsal part of the body-wall of each segment is called 

 the tergum. This name is also applied to the dorsal part of 

 the three thoracic segments collectively. 



