68 



ENTOMOLOGY 



Abdomen of female beetle, Cerambyx, 

 which the last three segments are used as an 

 ovipositor. After KOLBE. 



Orthoptera (to which order (Ecanthus belongs). In Collem- 

 bola, the embryo has paired abdominal limbs, and those of the 

 first -abdominal segment eventually unite to form the peculiar 



ventral tube (Fig. 12) 

 of these insects, while 

 those of the fourth seg- 

 ment form the character- 

 istic leaping organ, or 

 fur cula. 



Cerci. In many of the 

 more generalized insects, 

 the abdomen bears at its 

 extremity two or three 

 appendages termed ccrci. These occur in both sexes and are 

 frequently long and multiarticulate, as in Thysanura (Figs. 

 76,9, 10) and Ephernerida (Figs. 19, B; 84), though shorter in 

 cockroaches and reduced to a single sclerite in Acridiidse (Fig. 

 87). The paired cerci, or cercopoda of Packard, are usually 

 though not always associated with the tenth abdominal seg- 

 ment and are homologous with legs, as Ayers has found in 

 (Ecanthus and Wheeler in Xiphidium. As to their function, 

 the cerci of Thysanura are tac- 

 tile, and those of the cockroach 

 olfactory, while the cerci of 

 male Acridiidse often serve to 

 hold the female during copu- 

 lation. 



Extremity of Abdomen. 

 Various modifications of the terminal segments of the abdo- 

 men occur for the purposes of defalcation and especially repro- 

 duction. The anus, dorsal in position, opens always through 

 the last segment and is often shielded above by a suranal plate 

 and on each side by a lateral plate. The genital orifice is al- 

 ways ventral in position and occurs commonly on the ninth 

 abdominal segment, though there is some variation in this re- 

 spect. The external, or accessory, organs of reproduction are 

 termed the gcnitalia. 



FIG. 78. 



Abdomen of a female midge, Cecido- 

 myia leguminicola, to show the pseudo- 

 ovipositor. 



