NO. lO 



MORPHOLOGY OF GNATHOTRICHUS SCHEDL 



41 



THE ABDOMEN 



The chitinous skeleton of the abdomen shows httle specific modifica- 

 tion but it bears characters which are of importance in separating 

 the higher groups. The differentiation is mainly in the number of 

 dorsal plates or tergites and the development of the spiculum ventrale 

 in the females. The structure and the relative proportions of the dif- 

 ferent sclerites are illustrated in figures i, 2, 3, 20, 21, 22, 23, and 24. 



Dorsal plates or tergites. — All the tergites are normally covered by 

 the elytra. In the females seven and in the males eight tergites are 

 well developed. The first six tergites are more or less membranous 



Fig. 20. — GnathotricJius niatcriarius Fitch, male : Abdominal tergites, ventral 



aspect. 



I, 2, 3, 4, enlarged sections showing details of structure on the dorsal side; Epp, epipleurites; 

 Epp 7 and 8 fused with tergites; Sp, spiracles; T, tergites. 



and flexible in both sexes, yellowish in color, and covered with spinous 

 to toothlike armature on the external surface. The spinelike armature 

 is more medial and posterior on the plates. Near the anterior margin 

 the armature becomes more toothlike, forming broad plates armed 

 with minute spines posteriorly (figs. 20, Ti, 2, 3, 4)- These plates near 

 the median line on the second, third and fourth tergites are stouter 

 and not so densely placed. In the same tergites there is a reduction 

 of the chitinization, forming a membranous emargination. Still 

 another type of armature is found on the pleurites as illustrated in 

 figures 20, 4. The purpose of these armatures is doubtful. The in- 

 tersegmental membranes are colorless without any markings. Heavily 

 chitinized bands are situated near the posterior margin of plates two 



