206 



HIGH SCHOOL ZOOLOGY. 



named — Caloptenus femur-ruhrnm. Comparing it with the 

 cray6sh, we find that there are conspicuous differences both as 

 to the number and grou})ing of the segments, and as to the 

 number and nature of the appendages. Instead of a cephalo- 

 tliorax and abdomen, we find a head composed of four segments 

 (the number only to be arrived at from the aj^pendages), a 

 thorax consisting of three free segments (pro- meso- and nieta- 

 thorax), each of which bears a pair of w^alking legs, and the two 

 hindmost, each a pair of wings ; and finally, an abdomen of ten 

 segments without obvious appendages (Fig. 139). 



21. In the abdomen, the exoskeleton of each segment is divi- 

 sible into a stermim below, a tergnm above, and a lateral piece 

 on each side — the pleurum — coalesced with the tergum, and 

 only indicated by the stigmata. In the meta- and meso- 

 thorax (but not in the prothorax) a further differentiation is 

 associated with the attachment of the wings, for each tergum 

 or notum is subdivided into an anterior scittum and a posterior 

 sciitellum, while the independent pleurum is subdivided on each 

 side into an anterior epimerum and a posterior episternum. 

 Only the sterna of the head-segm(mts can be recognized, for 

 the dorsal part of the exoskeleton of the head (epicranium) be- 

 longs solely to the first segment. 



The thoracic legs are formed of 

 the femur, tibia, and three-jointed 

 *' tarsus," — these names must not be 

 supposed to indicate any homology 

 v/ith the parts so-called in Verte- 

 brates — articulated to the thorax by 

 the "trochanter," "coxa" and "tro- 



Fis. 140.— Maxilla and labium of „ 



Caloptenus. (After Packard), c, chantme, Dut the hcad-appendages 



cardo ; s, stipes ; 1, lacinia ; g.iralea; t , t rm 



p', maxillary palp ; sm.submentmn; are more Complicated, iheyem- 



m, mentum ; pf, palpiter; le and ]i, , i.i n^•c , ,i 



external and internal lobes ; p-', la- brace the tlltorm antenufe, thc 



^^^' strong cutting mandibles, the max- 



illae and the labium, which is formed of a second pair of maxillaj, 

 coalesced in the middle; lino (Fig. 140). Certain unpaired .struc- 



