PHYLUM ARTHROPODA — CLASS CRUSTACEA 



275 



missures. This portion, which consists of the fused ganglia from 

 segments three to seven, is known as the suh esophageal ganglia. 

 Ner\'es go from it to the mouth parts, first and second maxillipeds, 

 green glands, esophagus, and muscles of the thorax. Each segment 

 posterior to the subesophageal ganglia possesses a segmental ganglion 

 with branches to its respective appendages and muscles. The sense 

 organs include antennae, antennules, sensorj' hairs, statocysts, and 



^ _ _ Supraesoplmqeal qanqlion 

 - -Orcumesophaqeal connective 



'Subesophageal qanqlion 

 Thoracic ganglion 



ms^ Ring for sternal artery 



Jit abdominal ganglion 



Lateral nerve 



JVentral nerve cord 



Tegmental division 



Terminal cjanqlion 



Fig-. 156. — Dorsal view of nervous system of crayfish. Notice merging of anterior 

 thoracic ganglia with subesophageal ganglion. 



eyes. The antennae are tactile organs (sensitive to touch), the endo- 

 podite of which is a relatively long jointed filament. The exopodite 

 is much shorter and fan-shaped. The basipodite and coxopodite are 

 closely fused to the ventral side of the cephalic region. An excretory 

 pore opens to the exterior through the coxopodite of each antenna. 

 The hairlike processes along the edge of the carapace, on the legs, 

 and other parts of the body are also sensitive to touch. The anten- 



