CHAPTER XX 



MOUTH-PARTS OF INSECTS 



The type of biting mouth-parts has already been considered 

 in Chapter XVI, the forms here considered being more highly 

 specialized. 



SECTION XIII. SUCKING MOUTH-PARTS (TYPE, SQUASH-BUG) 



Material. Students should be provided with prepared slides of the mouth- 

 parts of the squash-bug. They should also have alcoholic specimens, as the 

 arrangement of the parts cannot be easily distinguished on the prepared slides. 

 Before studying the prepared slides the students should dissect out the mouth- 

 parts of an alcoholic specimen. With a pair of sharp-pointed scissors cut off 

 the ventral part of the head and place it in a thick glycerin solution, consist- 

 ing of equal parts of glycerin and alcohol. Then, under the lens of a dissect- 

 ing microscope, pull the long proboscis apart, noting the order of arrangement 

 of the different pieces. 



The mouth-parts of the squash-bug consist of a long, jointed beak in which 

 are found four long, threadlike setae. They should be compared with the 

 mouth-parts of the locust. 



1. Labrum. The labrum, or upper lip, is a long, triangular, 

 sharply pointed piece, with slightly serrated edge, and fits over 

 the groove of the lower lip. 



2. Mandibles. The mandibles are a pair of long, hairlike setae 

 with sharp-toothed points. They adhere very closely together, and 

 are .used in cutting into the tissues of plants in order to induce 

 a flow of sap. 



3. Maxillae. These closely resemble the mandibles and, like 

 them, lock together, forming a lancelike structure. They are used 

 in piercing plants, the same as the mandibles. 



4. Labium. The labium, or under lip, is formed into a long, 

 partially closed tube, in which lie the mandibles and maxillae. It is 

 made up of four segments of about equal length. 



Exercise 40. Make a careful drawing of the mouth-parts of the squash-bug, 

 showing the above details. 



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