88 ANIMAL BIOLOGY 



Behind the stomach lies the large heart which is enclosed 

 in a membranous sac called the pericardium. From the 

 heart there arise a number of arteries which extend forward 

 and backward and carry blood to all parts of the body. 

 Blood enters the heart from the pericardium through three 

 pairs of apertures, the ostia, which are provided with 

 valves to prevent its return. The blood which has been 

 forced by the beating of the heart, to all parts of the body, 

 passes into spaces between the tissues, called sinuses, and 

 finally collects in a large sinus lying along the ventral side 

 of the body. From here it passes to the gills and then 

 flows back into the pericardium. Thence it again passes 

 through the ostia into the heart to repeat its journey. 

 The blood of the crayfish is colorless and contains many 

 small bodies called corpuscles, whose functions will be 

 discussed in another chapter. 



Much of the waste matter in the blood is got rid of by 

 organs called from their color the green glands. They 

 are situated on either side of the esophagus and open at 

 the base of the large antennae. The reproductive organs 

 in mature individuals lie partly in the cephalothorax and 

 partly in the abdomen. Their ducts in the male open at 

 the base of the last pair of walking legs, in the female in 

 the base of the second pair in front of the last. It is not 

 difficult to distinguish the sexes of most of the higher crus- 

 taceans by the position of these openings. 



The nervous system is quite similar in its fundamental 

 features to that of the grasshopper. There is a brain over 

 the esophagus giving nerves to the eyes and both pairs 

 of antennae, and cords passing ventrally on either side of 

 the esophagus to a large subesophageal ganglion which 

 supplies nerves to the mouth parts; from this ganglion a 

 double chain of ganglia extends along the ventral side of 

 the cephalothorax and abdomen. 



