CHAPTER VI. 



THE MOUTH-PARTS OF INSECTS. 



The study of the mouth-parts of insects is of special in- 

 terest and importance because of the admirable illustration 

 of the principle of homology presented by the mouth-parts, 

 because in the classification of insects great importance is 

 assigned to the mouth-structure, and finally because of the 

 significance of the structural character of the mouth in the 

 study of the habits and economic relations of insects. 



The mouth-parts of the locust, the cockroach, and the 

 beetle have already been studied : they represent the biting 

 type of insectean mouth-parts. The student is, therefore, 

 already acquainted with the component parts of the mouth, 

 and with their character in the biting type. The mouth- 

 parts of many insects, however, are not of the strictly biting 

 type, but are modified to form an elongate tubular beak or 

 proboscis used for sucking liquid food, or are modified to 

 form a combination of the biting and sucking types. This 

 modification of the more generalized biting type varies in 

 the various insect orders possessing "sucking mouth-parts." 

 As a beginning in the comparative study of the sucking type, 

 the mouth-parts of a short series of insects, representing sev- 

 eral important orders, may be examined. 



In the examination of the mouth-parts dried specimens can 

 be advantageously employed. Remove the head from the 

 dried insect and boil it in dilute potassium hydrate (KOH) to 

 soften and partially bleach the chitinous parts. The length 

 of time of boiling will depend, of course, upon the degree of 



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