ACRIDIUM. 167 



scissors and place them in the watch-glass with the labrum, in 

 approximately their relative positions and study carefully. 



4. Pass a needle behind the remaining appendage, the 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. 



5. Remove the mandibles and examine their cutting margins. 

 Place them in position in the watch-glass. 



Make a drauring showing the structure of each of these appen- 

 dages. Arrange your figures as nearly as possible in the relative 

 positions of the parts. 1 



Internal Structure. Remove the wings, and before opening 

 the body notice the rather large, somewhat transparent tympa- 

 num on each side of the first abdominal segment, very near the 

 base of the leaping leg. The structure of the auditory organ 

 may be easily studied by staining, clearing, and mounting in 

 balsam. (See Packard's "Text-Book of Entomology" 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 dissection. 

 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 trachece. 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 marked by 



'The mouth parts of all insects that depend on biting off portions 

 of plants for food are quite 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. 



