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 2i per itr erne. 



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 zt^^\\^X\z^ prothorax^ ?ftesothorax^ 

 and metathorax. 



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

 consist typically of ten sclerites. Of t\\tse,four pertain to the 

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

 to the ventral part. 



The dorsal sclerites are named, beginning with the ceph- 

 alic, /r^i"^^^//////, scutum^ scutellum^ snid. 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 

 sternellum. The sterna of the three thoracic segments are 

 designated as the prosternum^ mesosternum^ and metasternum 

 respectively; and the sternella as th.t prostertiellumy ?nesoster- 

 fielliun^ 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 iergum. This name is also applied to the dorsal part of 

 the three thoracic segments collectively. 



