186 AKTHROPODA. 



Mouth Parts. — It has already been noticed that the mouth 

 parts serve to cut off pieces of leaves, which are then passed 

 directly into the alimentary canal. For such a purpose there 

 should be holding as well as cutting parts. 



1. Pass a needle under the lahrurn, which forms the upper 

 lip, and notice that it is hinged and that the end is lobed. It is 

 not supposed to be homologous with usual arthropod appendages. 

 With fine scissors remove it and place it in a watch-glass contain- 

 ing water. 



2. Immediately behind the labrum is a pair of hard, dark- 

 colored organs, the mandibles, that are used in cutting the food. 

 Their position should be carefully noted, but it will be better 

 to leave them in position until the other mouth appendages 

 have been removed. 



3. Situated by the side of the mouth and just behind the 

 mandibles are the maxillce. With a needle push one to one side 

 and notice that it consists of a somewhat flattened portion with 

 a jointed maxillary palp at one side. Carefully determine the 

 positions of the maxillfe with relation to other parts. What 

 possible uses are served by the two parts? Remove them with 

 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 drawing showing the structure of each of these appen- 

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



positions of the parts. ^ 



* 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. 



