INTRODUCTION. 



/Object and scope of this course of lectures, 

 i Method of study. 



3 Division of the Animal Kingdom into Branches. 

 ^ Branch Articulata.— The articulate type is an 

 elongated cylinder composed of many rings. The 

 alimentary canal is central, the circulatory system, 

 when present, dorsal, and the nervous system ventral. 

 /)-By variations in the number, size, form, and group- 

 ing of the rings, or segments, and their appendages are 

 produced all the forms of Articulates. 

 > Division of the Articulata into Classes. 



;'Class Insecta (Hexapoda).— Air breathing Artic- 

 ulates with three regions (head, thorax, and abdomen), 

 six legs, and usually wings. 



EXTERNAL ANATOMY. 



Body divided into three regions, — head, thorax, and 

 abdomen. 



Head, — Consists apparently of a single segment, but 

 in reality of several, (i, i8).* 



Appendages of the head. — ist. A pair of antenna;. 

 (For figures of different forms of antennae see 15, Atlas 

 pi. 8. On the function of antenna: see 16, II., 892; 



17, VIII., 577). 2nd. Compound eyes. (16, II., Qfio; 



18, pi. 9). 3rd. Simple eyes, or ocelli, (i, 25 ; 16, 



' See list of books, page 147. 



