ACRIDIUM 203 



labium, and see that it is hinged and forms the lower lip. 

 Remove it with scissors and place it in position in the watch 

 glass. You will find that it bears a pair of labial palpi, and 

 that there is a deep cleft along the middle line. These are 

 indications that the appendage is the result of the fusion of a 

 pair of appendages (the second maxillae). 



5. Remove the mandibles and examine their cutting mar- 

 gins. Place them in position in the watch glass. 



Make a drawing showing the structure of each of these 

 appendages. Arrange your figures as nearly as possible in 

 the relative positions of the parts. 1 



Internal Structure. — Remove the wings, and before open- 

 ing the body notice the rather large, somewhat transparent 

 tympanum on each side of the first abdominal segment, very 

 near the base of the leaping leg. The structure of the audit- 

 ory organ may be easily studied by staining, clearing, and 

 mounting in balsam. (See Packard's "Text-Book of Entom- 

 ology" or Brooks's "Hand-book of Invertebrate Zoology.") 

 Remove the dorsal portion of the wall of the abdomen and 

 thorax, and notice: 



1. The heart, which will be found attached to the portion 

 of the wall of the abdomen that has been removed, by means 

 of numerous radiating muscle fibers. You probably will not 

 be able to determine the structure of the heart in the dissec- 

 tion. Read this up, and determine what the radiating muscle 

 fibers are for. 



2. The space between the muscles and the viscera is filled 

 more or less completely by the fat body and the tracheae. 

 With a lens notice how the tracheae connect with the spiracles 

 and how they branch. Remove a portion of the tissue in 

 which you can see tracheae, mount it in water under a cover, 

 and examine it microscopically. Each tracheal tube is 



1 The mouth parts of insects that depend on biting off portions of 

 plants for food are similar. Directions for the study of the mouth parts 

 of the honey-bee are given further on, but the mouth parts of other 

 forms, such as the fly, butterfly, and bug, should be studied. 



