22 



extremity of the episternum of the metathorax and eephalad 

 of the base of the second wing is also a small, inconspicuous 

 sclerite ; this is the parapteron of the metathorax. It is even 

 less well-developed than the parapteron of the mesothorax. 



Spiracles and Peritremes. — Between the ventro-caudal 

 angle of the epimeron of the mesothorax and the fossa of the 

 leg is an organ which consists of a slit-like opening guarded 

 by two fleshy lips ; this is one of the openings of the re- 

 spiratory 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 peritreme. 



In the membrane connecting the mesothorax with the 

 prothorax 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, meso- 

 thorax, and metathorax . 



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

 typically oieleven sclerites. Of these, /^rpertaintothe dorsal 

 part_pf the segment ; three, to each lateral part ; and one to the 

 ventral part. 



The dorsal sclerites are named, beginning with the ceph- 

 alic, praescn turn, scutum, scutellum, and postscutcllum. 



Of the two principal lateral sclerlites, the cephalo-veutral 

 one is the episternum, the caudo-dorsal one, the epimeron. 

 The third lateral sclerite is small, is* articulated to the epi- 

 sternum near the base of the wing, and is called the parap- 

 teron. Paraptefa .have not been found in the prothorax ; 

 but there has been found on each side, in the membrane con- 

 necting this segment with the head, a pair of sclerites termed 

 the jugular sclerites. 



