NO. 2 THORACIC MECHANISM OF A GRASSHOPPER SNODGRASS 35 



the legs are really with the inflected pleura covered by the tergal ex- 

 tensions. The procoxal cavities are " open " behind, that is, there are 

 no postcoxal sclerotizations. Lying before the coxa of each leg in the 

 articular membrane of the leg base is a small trochantinal sclerite 

 (fig. 20 A, Tn). 



The protergiim. — The tergum of the prothorax, besides covering 

 the back and sides of its own segment, projects posteriorly over the 

 dorsum of the mesothorax in a wide, triangular lobe which fits between 

 the bases of the folded front wings. The top of the tergal bonnet 



Fig. 20.- — The prothoracic tergum and pleuron of Dissosteira Carolina. 



A, outer view of left side. B, inner view of right side, showing episternum 

 invaginated within the tergum. 



a, posterior edge of anterior fold of tergum ; b, anterior edge of posterior fold 

 (B, Rd) of tergum; c, d, e, the external vertical grooves or sutures of the ter- 

 gum (A) forming the internal tergal ridges (B) ; j,g, h, i, horizontal sutures 

 and their ridges connecting the vertical sutures and ridges. 



(fig. 20 A, T) is cut by a deep transverse notch somewhat before the 

 middle, and the part before the notch is compressed into a median 

 ridge. 



Each lateral area of the protergum is marked by a number of grooves 

 forming a definite pattern, and by two non-impressed lines. The first 

 non-impressed line (fig. 20 A, a) lies near the anterior border of the 

 tergum and runs parallel with it ; the second (b) extends downward 

 in a sinuous course just posterior to the dorsal tergal notch. These 

 two lines mark the limits of the inner folds of the anterior and pos- 

 terior inflections of the tergal wall (B, a, b) . The grooves of the tergal 

 surface (A, c-i) lie in the space between the two non-impressed lines. 

 They have no significance in themselves, but it is important to note 



