THE EXTERNAL ANATOMY OF THE LOCUST 



279 



d. The labial palpi. These resemble the maxillary palpi, but 

 consist of only four segments, which are attached to the palpifers. 

 These are located on each side of the mentum, below the attach- 

 ment of the ligula. 



5. Hypopharynx. The hypopharynx, or tongue, is located on 

 the floor of the mouth, between the maxillae. It is diamond-shaped 

 when viewed from above, and is covered with numerous small 

 taste setae. 



Exercise 5. Make a careful drawing of the mouth-parts, showing all of the 

 above-named structures. 



SECTION III. THE THORAX 



Material. Each student should be provided with both alcoholic and dry speci- 

 mens, and should remove the wings and legs from one side of the body only. 



1. Divisions of the thorax. As has already been noted, the 

 thorax is divided into three segments, known as the prothorax, 

 mesothorax, and metathorax. 



2. Prothorax. This is the segment to which the head is attached, 

 and may be divided into two regions, a dorsal region known as 

 the pronotum, and a ventral region known as the sternum. 



a. The pronotum. This is a bonnetlike piece extending over 

 the dorsal and lateral region of the prothorax. It is made up of 

 a fusion of four plates, which are indicated by the transverse sutures. 

 Anteriorly there is an opening corresponding to the occipital fora- 

 men of the epicranium. 



b. The sternum. The ventral side, or sternum, of the prothorax 

 is also made up of separate plates, or sclerites. The anterior sclerite 

 bears a spine on the median line. 



c. The prothoracic legs. These arise from the ventral, lateral 

 region of the prothorax. Their structure will be noted later. 



3. Mesothorax and metathorax. The sclerites of these two 

 segments are very intimately associated, and their structure will be 

 discussed together. The mesothorax is joined to the prothorax by 

 a membrane which permits of more or less movement. Posteriorly 

 the metathorax is joined immovably with the first abdominal seg- 

 ment. The mesothorax and metathorax form a strong, boxlike struc- 

 ture for the support of the wing and leg muscles. Like the prothorax 



