THE EXTERNAL ANATOMY OF THE LOCUST 277 



smooth, highly polished surfaces. If examined with a lens, the 

 surface will be seen to be made up of a number of hexagonal 

 areas, which are known as facets. 



c. The ocelli. These are sometimes called the simple eyes, and 

 consist of three very small, almost transparent oval areas. One of 

 the ocelli is situated on the front of the head just below the lowest 

 margin of the compound eyes ; the other two are placed in the 

 top of the impression which contains the bases of the antennae, 

 and in contact with the upper portion of the compound eyes. 



d. The antenna. These are two long, threadlike processes situ- 

 ated median to the compound eyes. Each consists of about twenty- 

 six segments. Each antenna arises from an oval depression known 

 as the antennary fossa, and is attached by a thin membrane which 

 admits of motion in all directions. 



e. The clypeus. This is a short, rectangular piece attached to 

 the lower straight edge of the epicranium. 



f . The month-parts. These consist of a number of separate parts 

 attached to the ventral region of the epicranium, and will be 

 studied in detail later. 



Exercise 2. Make an enlarged drawing of the front of the head, showing 

 the above parts. 



Exercise 3. Make an enlarged drawing of the side of the head, showing all 

 the parts. 



Exercise 4. Remove the head and notice the occipital foramen, or the 

 large opening by which the cavity of the head communicates with that of the 

 neck and thorax. 



SECTION II. MOUTH-PARTS OF LOCUSTS 



Material. In order to effectively study the mouth-parts of the locust each 

 student should be provided with prepared slides as well as with the alcoholic 

 specimens. As the parts are removed for study they should be mounted on 

 glass slides in a glycerin solution, and may then be compared with the pre- 

 pared mounts. The parts may be removed by grasping them at their attachment 

 with a pair of stout forceps and pulling them back at right angles to their 

 attachment. 



1. Labrum. The labrum, or upper lip, is a flaplike piece at- 

 tached to the lower edge of the clypeus. The free edge is deeply 

 notched on the median line. 



