INTRODUCTION. 9 



one, inasmuch as serial section -cutting and the highest powers of 

 the microscope must be employed. This, though highly inter- 

 esting in itself, is certainly not of vital importance to the young 

 student of forest entomology. It is, however, indispensable that the 

 salient features of head, thorax, and abdomen should in all cases be 

 well studied, and in some special instances be committed to memory. 

 It is upon these points that generic and specific characters depend. 

 The advanced student with a fair amount of leisure would do well to 

 study the internal anatomy of insects. 



The head is theoretically composed of a number of pieces, but in 

 general appearance is made up of one piece. On the under side it 



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Hoi'j<- phj 



Fig. 10. Typical mouth parts of insects. (Flatters.) 



bears the mouth, which is adapted either for biting or sucking. The 

 mouth arrangement separates the whole of the class Insecta into two 

 principal divisions viz., Mandibulata, or biting insects; and Haustel- 

 lata, or sucking insects. The biting mouth of the beetle and the 

 trunk-like proboscis of the moth are cases in point. Fig. 10 repre- 

 sents typical mouth parts of insects. 



The eyes in many cases form a prominent part of the head, and are 

 of two kinds compound and simple. The latter are termed ocelli. 

 In some insects as, for example, in the house-fly and hive-bee the 

 compound eyes cover nearly the whole of the head. The orbit of the 

 eye is covered by a transparent skin termed the cornea. An examina- 

 tion under the microscope shows that the surface of the cornea is 



