20 



THE CLASS OF INSECTS. 



simply a fold of the skin of the front part of the antennary 

 segment, and are not to be compared with the tergite or rudi- 

 ment of the eleventh segment of the abdomen. 



Now, since the arthropleural is the limb-bearing region in 

 the thorax, it must follow that this region is quite well devel- 

 oped in the head, while the tergal region, bearing the organs of 

 sight, sometimes of enormous size, is perhaps still more largely 

 developed ; and as all the parts of the head are subordinated 

 in their development to that of the appendages of which they 

 form the support, it must follow logically that the larger por- 

 tion of the body of the head is pleural and tergal, and that the 

 sternal parts are very slightly developed. Thus each region of 

 the body is characterized by the relative development of the 

 three parts of the arthromere. In the abdomen the upper 

 (tergal) and under (sternal) surfaces are most equally devel- 

 oped, while the pleural line is reduced to a minimum. In the 

 thorax the pleural region is much more developed, either quite 

 as much, or often more than the upper, or tergal portion, while 

 the sternal is reduced to a minimum. In the head the tergites 

 form the main bulk of the region, and the sternites are reduced 

 to a minimum. 



TABLE OF THE SEGMENTS OF THE HEAD AND THEIR APPENDAGES, 

 BEGINNING WITH THE MOST ANTERIOR. 



Preoral. 



First Segment 

 ( Antennary) , 



Tergal, 



Antennas, together with 

 the labrum, epipharynx, 

 clypeus, eyes, and ocelli. 



The Appendages. We naturally begin with the thoracic 

 appendages, or legs, of which there is a pair to each ring. The 

 leg (Fig. 25) consists of six joints, the basal one, the coxa, in 

 the Hymenoptera, Lepidoptera, and Diptera, consisting of two 



