386 Introduction to Animal Morphology. 



Each abdominal ring is divided into separate large 

 dorsal and small ventral, sometimes into lateral, 

 pieces ; thus the abdomen is distensible ; posteriorly 

 it often bears anal or genital appendages bristles, 

 spines, stings, forceps, vaginae, cerci. The abdominal 

 segments of the adult never carry limbs except in the 

 beetle Spirachtha eurymedusa, whose third, fourth, 

 and fifth segments bear two-jointed appendages. 



The larvae of Lcpidoptera and many Hymenoptera bear 

 small papillary processes, like the parapodia of worms, on 

 the somites In-hind the thorax, but the three anterior pair 

 alone exist in other larvae, as in Myriopods, and these alone 

 have adult successors. In the larvce of Phryganea the thora- 

 cic limlis are utili/.ed as assistants to the jaws. The wings 

 are structures comparable with the shells of Entomostraca ; 

 their motions in flight arc very rapid. The house-fly makes 

 300 strokes per second ( J/<//vv) ; the point of the wing de- 

 scribes a figure of 8. The muscles are striped, colorless or 

 yellow, and complexly arranged. 



The epiphar\ n^cal nerve ganglion is large and 

 lobed ; the hypopharyngeal is joined to it by short, 

 but to the first thoracic by much longer bands ; the 

 three thoracic ganglia may unite into one or two, and 

 the ventral ganglia vary from six to four. 



In parasitic insects the hypopharyngeal ganglion and the 

 ventral cord become closely united. The brain ganglion is 

 generally medially divided ; in ants and bees it is singularly 

 convoluted and lobed ;* the antennary, optic, and commis- 

 sural nerves arise from separate lobes. The ventral ganglia 



* Probably these maybe senscrial. /;:/; ;v'jr experiments indicate that 

 co-ordination of motion may reside in the hypo-, and will in the cpipharyn- 

 geal ganglia. 



