THE CRAYFISH AND ARTHROPODS IN GENERAL 205 



Attached to the base of the first maxilliped is a broad thin plate, 

 the epipodite, which has lost its branchial filaments. 



Excretory System. The excretory organs are a pair of rather 

 large bodies, the "green glands" (Fig. 101, 40) situated in the 

 ventral part of the head anterior to the oesophagus. Each green 

 gland consists of a glandular portion, green in color (40), a thin- 

 walled dilatation, the bladder (41), and a duct opening to the 

 exterior through a pore at the top of the papilla on the basal 

 segment of the antenna (42). 



Nervous System. The morphology of the nervous system of 

 the crayfish is in many respects similar to that of the earthworm. 

 The central nervous system includes a dorsal ganglionic mass, the 

 brain (Fig. 101, 25), in the head, and two circum-cesophageal 

 connectives (26] passing to the ventral nerve cord (27), which lies 

 near the median ventral surface of the body. 



BRAIN. The brain (Fig. 101, 25) is a compact mass larger 

 than that of the earthworm, and supplies the eyes, antennules, and 

 antennae with nerves. 



VENTRAL NERVE CORD. The ganglia and connectives of the 

 ventral nerve cord are more intimately fused than in the earth- 

 worm, and it is difficult to make out the double nature of the 

 connectives, except between segments XI and XII, where the 

 sternal artery passes through (Fig. 101, jo). Each segment 

 posterior to VII possesses a ganglionic mass, which sends nerves 

 to the surrounding tissues. The large sub-cesophageal ganglion in 

 segment VII consists of the ganglia of segments III- VII fused 

 together. It sends nerves to the mandibles, maxillae, and first 

 and second maxillipeds. 



The VISCERAL NERVOUS SYSTEM consists of an anterior visceral 

 nerve which arises from the ventral surface of the brain, is joined 

 by a nerve from each circum-cesophageal connective, and, passing 

 back, branches upon the dorsal wall of the pyloric part of the 

 stomach, sending a lateral nerve on each side to unite with an 

 infer o-lateral nerve from the stomato gastric ganglion. 



Sense Organs. EYES, The eyes of the crayfish are situated 



