I I O ABDOMEN chap. 



This is facilitated by an imbricated arrangement of the plates, and 

 by their being connected by means of membranes admitting of 

 niuch movement (Fig. 47, w, p. 88). In order to understand the 

 structure of the abdomen it should be studied in its most dis- 

 tended state ; it is then seen that there is a dorsal and a ventral 

 hard plate to each ring, and there is also usually a stigma ; there 

 may be foldings or plications near the line of junction of the 

 dorsal and ventral plates, but these margins are not really distinct 

 pieces. The pleura, in fact, remain membranous in the abdominal 

 region, contrasting strongly with the condition of these parts in 

 the thorax. The proportions of the plates vary greatly ; some- 

 times the ventral are very large in proportion to the dorsal, as is 

 usually the case in Coleoptera, while in the Orthoptera the reverse 

 condition prevails. 



Cerci or other appendages frequently exist at the extremity 

 of the abdomen (Fig. 47, n, p. 88); the former are sometimes 

 like antennae, while in other cases they may be short com- 

 pressed processes consisting of very few joints. The females of 

 many Insects possess saws or piercing instruments concealed 

 within the apical part of the abdomen ; in other cases an 

 elongate exserted organ, called ovipositor, used for placing the 

 eggs in suitable positions, is present. Such organs consist, it is 

 thought, either of modified appendages, called gonapophyses, or 

 of dorsal, ventral, or pleural plates. The males frequently bear 

 within the extremity of the body a more or less complicated 

 apparatus called the genital armour. The term gonapophysis is 

 at present a vague one, including stings, some ovipositors, por- 

 tions of male copulatory apparatus, or other structures, of which 

 the origin is more or less obscure. 



The caterpillar, or larva, of the Lepidoptera and some other 

 Insects, bears a greater number of legs than the three pairs we 

 have mentioned as being the normal number in Insects, but the 

 posterior feet are in this case very different from the anterior, 

 and are called false legs or prolegs. These prolegs, which are 

 placed on the hind body, bear a series of hooks in Lepidopterous 

 larvae, but the analogous structures of Sawfly larvae are destitute 

 of such hooks. 



Placed along the sides of the body, usually quite visible in 

 the larva, but more or less concealed in the perfect Insect, are 

 little apertures for the admittance of air to the respiratory 



